The relationship of Y/N and Mordred was the "normal" relationship that should be between brother and sister. When Mordred learned the truth behind Y/N, she had mixed feelings. If on the one hand she considered Y/N as someone born only to take her place, when she discovered what had happened to the King of the Knights and the man named Emiya Shirou from the aunt (and adopted mother) of Y/N, Illyasviel Von Einzbern, and his Magecraft teacher, Rin Tohsaka, as well as learning that behind the death of Y/N's parents was also Morgan's fault, began to see Y/N as a younger brother.

Mordred took her role as the older sister seriously. In addition, during the period of the Holy Grail War, Mordred began to form Y/N in the way of the sword. Y/N was the son of the King of the Knights and, although born as magus, had to keep the name of the prince of all the knights high. She admitted that Y/N was already at a good level, perhaps thanks to the fact that Y/N had already begun his training under the King of Knights ten years earlier.

"If this Rias Gremory, or whatever she's called, dares to do something like that again, she will receive a lesson that she will never forget," Mordred said, frowning at her forehead with irritation, "I'll show her what real hell is!"

On his way home, Y/N told his sister how Rias Gremory had tried to recruit him into his peerage by making him a devil. Needless to say, Mordred was not happy with this and wished to punish her for even thinking of doing this, but she stayed since Y/N had resolved the situation diplomatically.

"And how dare they call a piece of junk with the same name as the Sword of Promised Victory?!" Mordred protested after learning the story of the seven fragments of Excalibur, "a sword like Excalibur cannot break as if it were butter!"

Y/N nodded because he thought the same thing. If his mother knew about Excalibur, she would have had a heart attack or simply destroyed the fakes, which he would have done himself.

"Anyhow, no one here knows that I am the son of the King of Knights," Y/N said as the two siblings entered a communal garden "I don't trust the church and, in general, all the supernatural creatures of this world so I assumed the false identity of Y/N Emiya"

Mordred nodded and understood why. If the church found out that Y/N was in possession of a Holy Sword that could outdo any holy sword of that size, they would try to snatch it and find a possessor who could manipulate like a puppet to declare war against the fallen angels and devils.

Arriving at the door of the apartment, Y/N opened it. Upon entering, he saw that Xenovia and Irina had changed and were sleeping on a couch.

Slowly, Xenovia was the first to wake them up. "Sorry, I had fallen asleep," she said by making a yawn, "you took you longer than expected."

The look of Xenovia moved from her friend to the armoured knight next to him. "Who is he?" she inquired with suspicion.

"The reason I took so long," Y/N replied, "I met my sister on my way to the supermarket"

Irina, who had meanwhile woken up, approached with confused look. "Didn't you say that your family died and that your foster mother was somewhere in Germany?" she asked perplexed.

"I said that my father and mother died and that my foster mother was somewhere in Germany, but I didn't say anything about my sister," Y/N clarified to Irina.

Y/N said that he and his sister had separated when he moved to Kuoh, but that they kept in touch. He also said that he had accidentally met her on the street when he went to the supermarket. He finally told them that she had decided to pay him a surprise visit.

Mordred listened in disbelief to the lies Y/N told them. It was true that they had separated about three weeks ago and that her summoning was possible thanks to her sword which Y/N used as a specific catalyst for her summoning, but the story he told them was highly altered.

She had responded to the call, although it was very different from what she expected. Now she had a body made of flesh and blood as well as mana. She was like the King of Heroes during the Fifth Holy Grail War.

"However, Mordred," Y/N turned to her as she pointed to the two exorcists, "they are Irina and Xenovia, two exorcists I helped by giving them a roof over their heads."

Mordred's helmet melted, merging with the rest of the menacing armour. Irina and Xenovia were surprised at the striking similarity between Y/N and Mordred that they could almost be mistaken for twins, although both Y/N and the Knight of Treachery knew that they did not.

"I'm the big sister of Y/N," she said "I'm Mordred Emiya"

Mordred would not have ruined Y/N's efforts to keep the existence of Excalibur, Heroic Spirits and Y/N's Reality Marble secret. For this, she had to present herself in a credible way and what better way than to assume the false name of "Mordred Emiya".

The two exorcists looked at each other perplexed, but they nodded. They had no reason to doubt Y/N after he had helped them by giving them a roof over their head and exceptional food, not to mention the fact that he had recovered one of the stolen fragments.

Seeing that it was late, Y/N stated that he would go to the kitchen to prepare dinner for four people. Only to hear this, both Mordred and Xenovia began to drool so much that a drop of cold sweat fell from the forehead of Y/N.

--- Time Skip ---

Y/N and Mordred were in the first one bedroom. Y/N was sitting behind his desk to finish his schoolwork while Mordred was sitting cross-legged on the bed of Y/N. He was wearing a Y/N shirt and shorts since she had no clothes beyond her armour.

"So, when do we get to work?" the Knight of Treachery asked, wanting to test the strength of the supernatural creatures of that world.

Y/N smiled. That was Mordred. She was a battle maniac who was always looking for challenges worthy of her.

"As soon as I find Kiba Yuuto," the magus responded by turning to her "I don't know why, but it seems that the Rias Knight hates the fragments of Excalibur very much"

"It's obvious, isn't it?" Mordred grumbled "the mere fact that I dare bear the name of the sword of the King of Knight is an insult to my ears too"

Y/N nodded and said, "Even I think they are not worthy of that name, perhaps because they lack the fundamental component that is the desires and hopes of humanity." He got up from the chair and sit next to his older sister. "Even so, after the way I beat up that Freed, they will be forced to delay the plan," Y/N assumed.

After a fragment had been recovered and Freed was seriously wounded, Kokabiel and his collaborators would be forced to delay their plans.

"I have no idea where they are hiding except that they are in this town," Y/N continued "Since Rias' knight has not been seen since yesterday, I guess he went to look for them"

Mordred now saw the point of waiting. Why look for the enemy in person when someone else could?

"Fine, but what will I do to pass the time?" Mordred complained, bored at the idea of having to wait.

Y/N sighed wearily. "Do what you want, but remember that you have now received a second life since I managed to summon you with your real body," Y/N reminded her sister "don not die... again..."

Mordred could not help but smile, knowing that someone was worried about her. Suddenly, her gaze shifted to a knight-like statuette with the sword raised in the air that Y/N held in his hand.

"What is it?" she asked with curiosity.

"They're a bit peculiar pieces of chess. I received them when I arrived in this dimension," Y/N replied as he took from under the bed a box with seals made of runes above them. Y/N removed the seals and opened the cardboard box, showing its interior to Mordred "The devils use something similar to these to reincarnate people in their species"

Y/N explained the Evil Pieces system used by devils. Each piece was given an upgrade in terms of attack, defence, and magical power.

"But these are not evil pieces,". Y/N said, "I used structural analysis and found that they were forged using holy energy and dragon energy"

Y/N said that it was possible that the Heroic Pieces (so he called them to distinguish them from the evil pieces) did not change the nature of the subject in which they were implanted. An angel remained an angel, a devil remained a devil and a human being remained a human being. Nevertheless, he was not certain that the people in which they were implanted would not become Heroic Spirits when they died.

They offered the same advantages as the evil pieces:

The bishop improves his magical abilities to such an extent that the magician can use a multitude of offensive, defensive, healing spells, etc.

Rook guaranteed superhuman strength, increasing the parameters of attack and defence.

Knight gain greater speed and mobility, allowing them to perform attacks and manoeuvres at high speed.

The queen was the most balanced piece because it guaranteed all the traits of the Bishop, the Rook, and the Knight.

However, unlike the Evil Pieces, they guaranteed the dragon and the sacred elements.

"I can say that the King is missing," Mordred said, noting that there were only 15 pieces in the box "What happened to it?"

"The King Piece is implanted inside my body," Y/N declared, surprising Mordred "It did not give me any advantage in terms of magic or superhuman abilities, but allowed me to see through the various Holy Grail Wars"

Y/N gave an example by projecting Balmung, the Dragon Slayer Sword that belonged to hero Siegfried. Y/N had access to a Holy Grail war where seven Masters, flanked by seven Servants, faced seven other Masters for a total of fourteen Masters and fourteen Servants. Siegfried was the Saber of the Black Faction and, ironically, Mordred was the Saber of the Red Faction.

"Well, it's a big advantage for you that you have an unlimited arsenal of weapons," Mordred commented, "but I see you haven't used them on anyone and that's a bit of a waste." Then an idea came to her mind, idea that she immediately explained. "use one on me," she said.

Y/N blinked a couple of times, clearly surprised by Mordred's request. The fear of turning a human being into a Heroic Spirit stopped him from recruiting people. He would only use them if a person were sure to accept that risks or was dying. In that case, if he could have saved that person, he would have done so without any hesitation.

But in this case, it was Mordred we were talking about. She was already a Heroic Spirit and would return to the Throne of Heroes when her life would come to an end. But was it right to submit her again as at the time of the Holy Grail War?

"Are you sure of this?" Y/N asked, puzzled.

Mordred nodded, "You're wondering if the piece doesn't turn the unfortunate into a Heroic Spirit when he or she dies, and I can understand that you don't want to condemn him or her to eternal Holy Grail Wars." Mordred put her right hand on Y/N's left shoulder and smiled. "But I already am one and that means I can only earn by having one of these pieces. I will get the Holy and the Dragon elements, becoming stronger than I am now," she said.

Y/N brooded for a few moments before giving an answer to his sister. Looking at the face of the Knight of Treachery, Y/N saw no sign of doubt in her facial expression.

"Fine," Y/N nodded and sighed before peering into the pieces.

Since we are talking about Mordred, rook, knight, and bishop were out of the question. The only pieces that could go with her were the Queen or one of the eight pawns. In the end, Y/N decided that the best choice was the pawn for someone like Mordred.

He took one at random from the box, leaving Mordred disqualified.

"Are you kidding?" The former Saber class servant asked with a frown "why of all the pieces just the pawn and not the Queen?"

"Because the pawn has something the queen doesn't have. It's something that makes it unique," Y/N answered sighing "it gives you the ability to promote in all the other pieces except the King piece"

Now Mordred was interested. The pawn had the ability to promote her in one of rook, knight, bishop, and queen, but it did not end there since she would gain the boosts of the piece chosen for the promotion.

"For an exceptional swordswoman like you, who has extensive experience of the battlefields and a strength that is already monstrous as it is, I think the pawn is the most suitable piece for you even if you will need my consent to promote yourself" Y / N ended as Mordred proudly swelled his chest for the description which, according to her, was more than appropriate "but you should have learned that I am not one who brakes your desire for battle except due to extenuating circumstances"

"I understand and this puts a goal in front of me," Mordred said, now convinced to become the Pawn of her younger brother, "I'm going to be the strongest pawn of all time, in spite of those filthy devils"

Y/N started giggling, but soon it became a laugh. That was Mordred at the end of the day, and he could not do anything about it. He just prayed she would not kill someone for it.

A few moments later, Y/N and Mordred were facing each other. The Y/N room was reinforced and soundproofed thanks to the runes, so he did not have to worry about destroying the room or that Irina and Xenovia heard what he did.

Now the problem was how to make the ritual work. Y/N was struggling until he tried something that the mysterious voice had repeated a few times in his dreams.

"An oath will be placed here. Your destiny is my destiny and my destiny is entrusted to your sword," Y/N sang while the pawn piece shone with red and gold light in his hand "If you accept the conditions, answer me now, Mordred!"

Mordred looked puzzled at that strange magical phenomenon. She honestly believed that everything was going to blow up, as in science fiction movies. She had no idea how to respond, maybe anything was fine, but then she had a strange feeling and the words magically entered her mind.

"I, Mordred Pendragon, accept and swear to serve you. I am your pawn and you are my king. Let it be my sword that forges your destiny," she said, repeating the words that had been charged in her mind by an unknown force.

Suddenly, the pawn piece began to levitate, and the golden and red light became more intense. A few moments later, it rushed into Mordred's body, entering her as if to merge with her essence. Her body radiated a holy and draconic aura for a few moments before vanishing altogether.

"That's all?" Mordred asked, arching an eyebrow for confusion. "I was expecting something like fireworks and explosions," she said with an air of disappointment.

"At least I won't have to explain to the owner how I destroyed the house," Y/N said sighed, relieved that nothing had been destroyed, "Without a workshop, I must be cautious when working on Magecraft not to reveal the existence of the moon-lit world"

In fact, if humans had discovered the existence of the supernatural world, as well as magic, chaos would probably have broken out and a new witch hunt would have begun. Y/N was only relieved that no one, with the sole exception of him, knew the existence of the Heroic Spirits.

"However, for the moment, I will try to keep a low profile," Y/N said by putting the other Heroic Pieces in their place, with all the seals of the case, "I don't want to have the greedy eyes of some other devil or fallen angel"

"In case that's not the case," Mordred smiled like a shark, "I'll have fun with them"

When Mordred said, 'Have fun with them', she meant to tear them apart in the true sense of the word. Y/N could not help but sigh for this.

"It's better that I go to bed," Y/N tirelessly said as he wrapped himself in the futon since Mordred had taken his bed.

--- Time Skip ---

The next morning, Y/N thought it would be the normal school day and at the end of school activities, he would head home. And yet, the day was over, and he was in the Student Council Office.

The president is a third-year student named Sona Shitori. She is a girl with a slender figure, black bob hair and purple eyes. She is wearing round glasses.

Standing to her right, she was the vice president of the student council, a girl named Tsubaki Shinra. She has long black hair reaching up to her knees and light brown eyes. Like Sona, she wears a pair of square glasses.

"So," Y/N asked nervously massaging the back of the neck, "can I know why I'm here? It's certainly not for my academic performance or my behaviour"

"You're right, Mr. Emiya," Sona responded by adjusting her glasses, "Actually, I just wanted you to answer some questions"

Y/N sighed and watched Sona intensely. From the beginning he knew that the Student Council was composed of only devils and the girl in front of him was the one who worried him the most, although Y/N was not impressed by her power.

"Do you want to ask me if I want to join your Peerage?" Y/N asked, much to the surprise of Sona and Tsubaki. "Yes, I know you're all devils and you followed me wherever I went," Y/N said, "Whoever you sent must work on the surprise factor."

Sona smiled. As she suspected, Y/N was not a fool and as a wizard he was skilful since he perceived that she too followed closely. Like Rias's familiars, even her familiars could not see what Y/N was doing in the house, although Sona knew it was hosting two members of the church.

"That's not what I wanted to know. I spoke to Rias and she told me that you are a magician," Sona said by taking the serious look, "and I want to ask you if you're in league with the church. I know you are in contact with two exorcist"

"No, I'm not," Y/N answered with a serious voice "I met Xenovia and Irina by chance on the way home. I helped them and now they've settled in my house"

"Why didn't you kick them out?" Sona asked.

"Because they needed help and I refuse to leave a living being to its fate," Y/N replied, surprisingly Sona and Tsubaki.

"And when did you save the Rias' Knight? Why did you do?" Sona asked, with a smile due to the curiosity of his answer.

"Because I wanted to do it," Y/N responded with a firm and powerful voice "I don't need a reason to save a life that can be saved"

Sona and Tsubaki's eyes opened wide for surprise. His behaviour could be translated as hypocritical because nobody did anything for nothing. Everyone always had an ulterior motive. Yet, seeing his face, Sona realized that he was serious by saying that he did not need a reason to save someone.

"Well, I want to give you the benefit of the doubt since you saved Kiba from safe death," Sona said before moving on to the other topic of interest. "Now, would you mind explaining to me what your magic is?" she asked.

Y/N nodded since he had no problem talking about this. After all, only his father, he and probably his descendants can have access to reality marble. "I use a magic called Gradation Air," Y/N began to speak "I can materialize objects starting from my imagination through the manipulation of magical energy."

Sona nodded, but she saw a flaw in all this. "Wouldn't the object fade in time?" she asked, raising an eyebrow for perplexity.

Y/N nodded in response to Sona's question. "My father developed a personal version called Tracing which differs significantly from normal Gradation Air in that I not only recreate an object in form and substance, but also in its history," Y/N said then pointing to the chess placed on a shelf on the right of Sona "I can tell you that those chess are a gift from your parents, Lord and Lady Sitri, and that you often use them to play friendly games with Rias Gremory. The result always goes in your favour"

Sona's eyes opened wide for the third time and her jaw fell to amazement. She could not believe that one look was enough for him to get all that information.

"It must cost a lot of magical energy to do such a thing?" Sona asked.

"In my case, it depends about the type of object," Y/N replied "Although I am able to manipulate the four elements, I also have a particular affinity which allows me to recreate some objects with little consumption of magic energy"

"I understand, Y/N" Sona nodded "Would you mind giving me a demonstration?"

Y/N nodded and threw a sword with a golden handle. Y/N put the sword on the desk. That sword was the demon and Dragon Slayer sword used by Sigurd, Gram. Besides, only the most powerful of holy swords can hope to stand up to the challenge with it.

Sona continued to admire the sword and, as Y/N had said, the consumption was minimal. Moreover, the rate of decay of the weapon was so slow that Sona could only assume that it would take a couple of days for it to disappear. However, before she could ask for it, Y/N had already disappeared from reality with a simple blink of an eye.

"This conversation was very interesting, but I would like to take my leave now," Y/N said, getting up from his chair and walking to the door. However, he stopped and said something else: "I hope you understand that I am not going to do anything against you, Rias, and your Peerages, unless you threaten me. In that case, I won't be very nice"

That said, Y/N left the student council room. Sona watched with awe the magus come out because, although Y/N had said much, he had not said everything he could do. He still understood that it was better not to antagonize him or dared not imagine what he could do.

"It's all right, President Sona?" Tsubaki asked perplexed.

Sona sighed and nodded. "May I feel that he is human, but a part of him is not," Sona thought mentally "Perhaps his affinity involved a mutation in his body?"

----------------------------

As soon as he crossed the school gate, Y/N felt a familiar presence. Surprisingly, Mordred was leaning back against the wall. He was wearing a red half-sleeved shirt, ripped jeans, and leather boots.

"What are you doing here, sis?" Y/N asked surprised.

"It was boring to stay home," Mordred responded with a shrug of her shoulders "I thought I'd surprise you"

Y/N just smiled.

"Anyway, why did it take so long to get out?" Mordred asked "I thought I had been kidnapped by a dirty devil"

"Why does everything have to end in a massacre for you?" Y/N sighed as he heard a chuckle coming out of his sister's mouth "Anyway, I had to explain to the Student Council President that I have no intention of doing any harm to her and her peerage"

"And how did you do it? Did you use threats?" The Knight of Treachery asked with a grin.

"I explained generally speaking what I can do and a little practical demonstration," Y/N replied, much to Mordred's disappointment "and then threatened that it would end badly if they tried to use some dirty trick with me"

The two siblings walked home unaware that a figure was flying over their heads. She is a little girl with long black hair up to her hips and grey eyes. She wears a Gothic Lolita dress.

"A world of silence. I would like to return to the Dimensional Gap that is my home and recover that silence..." The little girl murmured as her inexpressive gaze remained fixed on Y/N. A little smile was impressed on her face. "Thinking that he would bring someone like him, whose soul is a silent world as much as the dimensional gap" she continued.

----------------------------

Upon arriving home, Y/N felt the presence of someone inside. He expected to be Xenovia and Irina as usual but realized that it was not so since he could clearly perceive that it was a demonic signature.

He projected a sword and, as an inevitable consequence, Mordred re-equipped Clarent. Y/N whispered to Mordred to be quiet because the intruder could be dangerous and attack them when he/she heard them enter.

Y/N slowly opened the door and entered. Slowly he went to his bedroom and felt the demonic signature inside. Much to his surprise, he saw a black cat sleeping on his bed curled up on itself.

"A cat?" Y/N thought puzzled how is it possible that a cat entered the house.

Y/N turned to Mordred to ask if she had let it in, but saw that she was shaking his head, denying that she had done anything of the sort.

Turning to the black cat, Y/N wondered why it emanated such demonic power, superior to any other devil he had encountered. Without being perceived, Y/N took the black cat for the fur coat which, as a result, woke up.

"Good evening," Y/N said with his eyes closed and a creepy smile "I hope you enjoyed sleeping on my bed"

Suddenly, the cat started to wriggle, forcing Y/N to let go. To the great surprise of the magus and his sister, the cat also changed shape. Now, a voluptuous-bodied girl with cat ears and tail was lying on the bed of Y/N. She has black hair and hazel eyes. Her clothing consists of a black kimono, a yellow obi, a series of golden pearls and a richly decorated headband. The kimono has a red interior and is open behind it.

"Who the hell are you, filthy cat?!" Mordred asked, frowning at her forehead with irritation.

If Y/N had not told her to stay calm, she would have tried to kill the cat-woman by now.

"We are susceptible, huh?" the cat-woman joked, seeing the irritation on the face of the Knight of Treachery.

Mordred was now even angry for her presumption and nothing would have stopped her from tearing the cat-woman to pieces and making Clarent wet in her blood.

Before the cat-woman could say or do anything else, she found chains around her. Now, if it were normal chains, she would have freed herself easily, but her face was covered with wonder when every effort to free herself went in vain.

"What...?" she interrupted when she found the sword of Y/N pointed at her.

"Who are you and how did you get into my house?" Y/N asked, with deadly serious voice "Don't lie because it will be the end for you!"

"My name is Kuroka," she said with a smile full of lust, dismounted by the tinkling of the sword that was now inches from her throat. Kuroka swallowed nervously. "Okay, you won," she said, "I was hanging around the abandoned church where I saw you performing that strange ritual that she came out of. I was curious to know more, so I followed you, but due to the presence of those two exorcists and three fragments of Excalibur, I had to wait for them to leave in order to enter."

"Okay," Y/N replied by offering the benefit of the doubt, "but you'd better forget what you saw"

"And why should I do it?" Kuroka replied before she gasped at the metallic rattle of the sword she had near her neck.

"Hey little brother, let's kill her and the problem will be solved," Mordred suggested.

Y/N admitted that killing Kuroka would solve the problem. Information about the ritual summoning of the Heroic Spirits had to remain secret to the supernatural world to avoid the chaos that would ensue if a war broke out between heroes who could easily raze a city to the ground.

"I give you three options and you have to choose one," Y/N said, "The first option is to erase your memory about what you saw. The second one is that I kill you here and you take the secret to your grave."

"And the third option?" Kuroka joked.

"The third is that you stay here for the rest of your life and don't divulge what you saw last night" Y/N replied.

Okay. Kuroka did not like any of the three options, but she did not have much of a choice since she could not get rid of those strange chains that blocked her movements and the sword that was ready to pierce her throat.

"Take care of me," Kuroka joked.

----------------------------

A/N: Here is the third chapter of this story. I hope you enjoy the idea of the Heroic Pieces and I'm sorry for those who are disappointed that I chose to put Mordred as a pawn, but I already have someone in mind for the position of Queen.

For the time being, these are the safe members of the Hero Faction of the DxD:

King: Y/N Pendragon

Queen: Valerie Tepes (I consider Fem Gilgamesh in this role, but I think putting the King of Heroes in Y/N's Peerage is a mistake. I think that she would hardly submit to someone she considers inferior to her)

Rook: Rossweisse

Rook: Mashu

Bishop: Kuroka

Bishop: Tamamo-no-Mae (Sixth Holy Grail War)

Knight: Xenovia

Knight: Jeanne D'Arc (Fate/Grand Order)

Pawn: Mordred (Sixth Holy Grail War)

Pawn: Jack (Sisth Holy Grail War)

Pawn: Brynhildr

Pawn: Cao Cao

Pawn: Ana (Fate/Grand Order)

Pawn: Atalanta (Fate/Grand Order)

Pawn:

Pawn:

Harem: Mordred, Xenovia, Tamamo, Kuroka, Rossweisse.

Important:

1) Gilgamesh will come from a parallel world such King Arthur in Fate/Prototype and she will be a separate existence from Gilgamesh of Fate/Stay Night.

2) At the beginnig I thought of putting FGO's Valkyrie in the Peerage too, but in the end, I preferred to remove them because I think Rossweisse and Brynhildr are enough, with the last one being considered as a sempai of Rossweisse.

3) Cao Cao will be the only male member of the Peerage.

4) Morgan will be an ally in this story, putting aside her grudge with Artoria and helping her nephew (don't ask me to add her to the Harem because Mordred is already enough for incest).

5) The last two pawns will be respectively a Fallen Angel and an Angel. I want at least one for each of the biblical races to be part of the group. Kuroka represents the part of the devils.