I have a important note at the end of the review so please read it. Thank you ahead of time. This OC is by KakikomiSama I hope you like it.

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Name: 
Himura Keiki (緋村慶希)

Nice name

Meaning of Name:
Keiki: combination of 慶 (kei) meaning ‘celebrate’ and 希 (ki) meaning ‘hope’
Himura: combination of 緋 (hi) meaning ‘scarlet, dark red’ and 村 (mura) meaning ‘town, village’

Nice combination of a name, it's very well thought out.

Generation:
Itachi Uchiha's Generation

Nice, it's good to see a different age group than the usual.

Age:
Post Naruto - 4-16 years old
Part 1 - 18-19 years old
Part 2 - 21-22 years old
The Last - Deceased

Oh she died? I wonder how.

Gender:
Physically, Female
Mentally, Male

Oh so he is originally born a girl? But how does one thing like a man? How does a man think to have a mentality like one?

Status:
Deceased after Fourth Shinobi World War

Oh did he die in the 4th great ninja war? Let's continue and see.

Birthday:
October 12th (Libra)

Oh a Libra nice.

Blood Type:
O-

Nice

Clan:
Himura (90% Mercenary, 10% Shinobi)

Oh ok but how can you be 10% Shinobi like it's a race? You could say they trained a little in being a Shinobi but being a Shinobi is not like being white or black or a hyuga or Uchiha.

Classification:
S-rank
Missing-nin

Oh ok

Affiliation: 
Kirigakure (former village)

Oh ok, what village are they in now?

Ninja Rank:
High level Jounin

Cool

Relatives:
Himura Chika | 緋村千花, Scarlet Village of Thousand Flowers | Mother | Deceased, Death From Severe Injury
Himura Ryuunosuke | 緋村龍之介, Scarlet Village of Dragon Forerunner | Father | Deceased, Death From Severe Injury

Nice and thanks for giving me the life status and the cause of death.

Appearance:
When Keiki lived with his clan, he had long dark blue hair that was always in a crown braid or just let down to his waist. His parents forced him to wear kimonos every day, most being a pinkish color. When he finally left, Keiki cut his long hair to the back of his neck, leaving enough to be pulled into a ponytail with a lilac colored ribbon. Keiki has golden yellow eyes and fair skin with a few scars from his journey.

I already talked about the word fair as a skin tone before. When it comes to skin no color is fair. It's white, black, light skin, etc. Because what would be fair about a skin tone. Not everyone has it. Other than that, the appearance is great.

Currently, Keiki has messy, short dark blue hair with bangs reaching his jaw and framing his face, golden yellow eyes that are becoming a bit narrowed and fair skin with a bit of a tan tint to it.

Nice, it's easy to imagine as well I can picture him in my head.

He has muscular yet lean build, being around 172 cm (5’6 ft) and being around 58 kg (127.8 lbs.), his body showing he was built for speed and stamina.

A beautiful height to weight ratio that is also perfect for a track star. His built makes him great for speed and stamina.

He usually wears a blue, short sleeved yukata shirt, a dark blue string tying the shirt shut. For bottoms, he wore navy blue pants with ankle shinobi shoes with a steel toe. 

A easy to imagine outfit and it fits his face and build.

On the right side of his waist, Keiki has a sheathed katana tied to him. The saya (scabbard) is a dark blue color, with paler blue markings along the sides. The katana itself has a royal blue handle with lighter blue ray skin and a red cord wrap around it, which has a dark red bell attached to it. The guard of the katana is royal blue as well. The blade collar is a normal blue. The blade itself is a stormy gray color, the edge pattern being uneven and jagged. He named this weapon 'Kurai Sōon', or 'Dark Maelstrom'. Keiki usually uses this weapon.

A beautiful description that is straight to the point. It has everything about his sword and is well detailed. It is a great weapon. Also thanks for stating it as his usual weapon.

His second weapon, a sword, is attached to the the left side of his waist. The saya is a a yellowish silver color, with a strip of blue along the sides of it and the cord wrap being a soft golden color. The handle of the sword is a light blue and silver color, with a golden yellow string and a silver bell attached to it acting as the hanging cord. The guard is a golden color, while the blade collar is a soft silver. The blade itself is a silver-white color, having a smooth and sharp edge pattern and a silk appearance. This sword is called 'Seinaru Hikari', or 'Holy Light'. Keiki only ever uses this weapon if he is against an opponent stronger than him. Scars litter his legs and torso, the worst scare being a jagged scar going down his right shoulder to the end of his back. He covers this up with white bandages wrapped around his torso.

This is also a beautiful and well detailed description of his secondary weapon. I also like how you have the names of each sword contrast with each other as light and dark. It's a great idea.

Personality:
During his childhood, Keiki was a very quiet and observant as a child. Instead of hanging with the other children his age, Keiki would always be found somewhere high up, observing how the others react. He did this because he always felt different, like he was born into the wrong body. So he watched the others, wanting to see if anyone else felt the same way. When he realized no one else was the same as him, Keiki tried his best to be the perfect ‘lady’ for the clan, but realized it just made him very depressed and unsociable, which led him to telling his parents about his situation. When they expressed their disgust towards Keiki, Keiki became dull and emotionless, looking like a doll as his parents forced him into things he didn’t want to wear and forced him to do things that he disliked.

Oh so he is the depressive type. This seems like it should be more in the background info but his personality shines in this description. Having things forced on you is the worse and dealing with that all your life with no one standing up for you is terrible. His character shows itself in this little paragraph.

The only time he was ever himself was when he was training like a male. During that time, he would be entirely focused on his objective, and when he got it down good enough, he would cheer himself up and continue on. The days he was locked up, Keiki became miserable and hateful, hating his family for locking him up and forcing him to become something he wasn’t.

Oh so he soon developed hatred as a trait as well. From being locked away I can see why and the fact that no one still listens to him is a perfect reason why he should have hatred.

At age ten, he showed good abilities in acting as he managed to convince his family little by little that he believed he was female and not male. When the time came, Keiki severely injured his ‘parents’ and then left for Kirigakure. There, he showed great resolve to become a shinobi, having a good mindset and being able to control his emotions perfectly. He wasn’t too intelligent, but he was intelligent enough that he could up with good strategies on the spot. He became known for his speed, as his body was lean yet muscular, most muscles being in his legs for the speed.

Nice but were his parents ninjas? If they were how did a ten year old injure them? If not than its fine.

When he was with Itachi Uchiha, he showed a side of himself he never showed others. He showed Itachi his caring and loving side. He truly cared for the Uchiha, the other being the first true friend he ever had in his life, and loved him dearly.

So he had a secret side of loving and caring. That's great, I would recommend if he never shows it, have him dream of one day showing to someone, so that people know he has a loving side and isn't like Sasuke. The side is great, amazing actually but letting people know a head of time he has it if he is going to be in a story or just in the background is a good idea. The reason why is cause there are people who will call him out for suddenly having a caring side out of no where but if they see he has always had it and never showed it to anyone but the audience seen it through something like dreaming or thinking than that would solve the problem.

When sometimes alone, Keiki would be wise, always looking at the night sky with sadden eyes filled with pain and sorrow. During these times, Keiki would wonder about his purpose in life, his reason for everything he has ever done, and then wonder if he would ever become the man he wants to be someday.

That is something regular people do as well. Wonder their purpose and wonder if they could live up to their own expectations. This gives him some realistic traits we see in the real world as well. Good job.

Abilities:
Primary Release - Water
Secondary Release - Earth
Keiki mainly focused on his primary infinity, with some earth techniques to keep him safe from other natures, especially lightning. He has made up a few of his own water techniques, one of the known one’s being ‘Water Release: Twin Snakes’ which is where he makes two long water whips, then forming them into two snakes that strike at the opponent like whips but with snake heads. His lesser known jutsu is ‘Water Release: Purifying Sin’ which is where he uses the water to heal others wounds. He incorporates his water release and earth release with his kenjutsu style and taijutsu. Before he passed, Keiki had around high level jounin ninjutsu, medium-high chunin level taijutsu, medium-high jounin level kenjutsu, low-medium genjutsu, and high amounts of stamina. 
 
Nice, also his move Twin Snakes sounds like the move from hunter x hunter used against Gon and Killua during the heaven's arena arc. You can check it out if you want. The man who used it was in a wheel it sounds the exact same so if it is based on that move than a reference is needed. References are great and if it isn't than you and the creator of Hunter X Hunter have great minds.

Back Story:
Himura Keiki was born as the first child of Himura Chika and Himura Ryuunosuke, who were the matriarch and chief of the civilian clan Himura. Most members of Himura clan are civillians, but the main branch of the clan end up becoming shinobis since most were being killed in the Warring Clans Era. Keiki, as a young child, was born female and was adored by the clan because of her sweetness and innocence. But Keiki didn’t think of himself as female, he thought of himself as male. As such, Keiki told his parents about this, and his parents were disgusted. They were teaching Keiki to be a matriarch, and they didn’t do anything to change that when they learned Keiki thought of himself as a male. Instead, they forced more matriarch work on him, believing if he saw his female side, he will get out of this ‘state of mind’.

Oh so his parents didn't agree with his choice to be a man. It is difficult to have to deal with you being the odd ball when it comes to sexuality. It is even heartbreaking when your own parents don't accept your choice. This brings character to his...well...charcter.

This made Keiki depressed since he was being forced to become someone he believed he wasn’t. So while he trained during the mornings and afternoon in matriarch, Keiki left during the late afternoon and nights to train as chief and a shinobi, dressing as a male as well instead of those silky kimonos and dresses his mother forced him to wear.

Oh so he is kinda pulling a Zelda when she turns into Sheik. That is cool and unique.

When Keiki was 7 years old, Ayame and Ryuunosuke found out about Keiki’s advancement and when they did, they punished him by locking him up in his room with seals keeping him at bay. The only time he ever saw people were his parents who came to teach him the matriarch responsibilities, how to act like a lady, feed him, bathe him, etc.

So this was torture to him because he was being forced to be someone he wasn't. Good job, it also shows the realization that not everyone even your own family may not accept you.

The other times he saw people were his aunts, uncles and cousins who only came to laugh at him, calling him hurtful words and how he would probably die locked up. This caused Keiki to come to despise his family, hating them for forcing him to become what they wanted him to be.

He has the right to be mad and hate them.

When Keiki turned ten, he was finally let out of the room so they can marry him off to a potential suitor to be the chief of the clan. But things didn’t go planned. Once he was free, Keiki fooled them into thinking he thought of himself as an actual female for a month, slowly gaining his families trust little by little. When the day for the ceremony came, Keiki used the skills he taught himself through stolen books before he was locked up and managed to fatally injure his mother and father. While everyone was focused on the fact a ‘female’ managed to use shinobi skills, Keiki quickly left the scene and headed towards Kirigakure, where he would stay for 3 years to learn as much as he could as a shinobi.

So he used his brains to outwit and gain the trust of his family. This brings great character development to the scene as well. It shows how he grew into a shinobi and how he knew he still wasn't ready.

Once he believed he was good enough to defend himself, Keiki defected from Kirigakure and became a missing nin at the ripe age of 13, using pills and injections to help with his body to develop like male while at the same time trying his best to get use to the menstrual cycle. When Keiki was exploring a small village near the Land of Fire, he met a boy named Itachi Uchiha, who was on a mission and was scouting the area.

Oh so he deals with the menstrual cycle. A lot of people seem to forget about that in anime. I'm glad you remember that a girl has a period every month.

Keiki found Itachi to be interesting, so he offered to help Itachi so he could learn more about him. While Itachi was hesitant, seeing as Keiki was wearing a Kirigakure headband with a slash through it, Itachi agreed since he too was interested in Keiki. As the two worked together, Keiki was initially afraid of Itachi disliking him when he found out his physically sex, but instead, Itachi just seemed curious about it before telling Keiki he would accept him as he was, since to him genders shouldn’t matter. This caused Keiki to quickly warm up to Itachi throughout the weeks as they did the mission, and once it came to an end, Keiki gave Itachi a picture of two of them eating dango so he would remember him.

Cute, Itachi is a nice person through the series but he is also very cautious. I like how you had him notice the slash through the headband and didn't attack to see what would happen. It's cute that they have a picture.

Before Itachi went over the border, Keiki gave the other a hug, and while it embarrassed the both of them, he also gave a small kiss to Itachi. While Itachi was both confused, shocked and embarrassed, Keiki told Itachi that he grown to start liking the other male, and that Itachi was Keiki’s first crush/love. He also told Itachi that he knew if he said anything about these feelings, it would cause a lot of troubled thoughts to Itachi, so he didn’t say anything until now. While Itachi was troubled at learning this new info, he told Keiki he was happy that Keiki gained feelings for him, since he only ever had experience with ‘fangirls’ who only liked him for his appearance/abilities of a shinobi, and that while he does not fully understand his own feelings for Keiki, he would always remember the other’s feelings. This made Keiki happy, giving Itachi another kiss before he left the other. He was sadden that he had to depart from Itachi, as Itachi was his first friend and crush, but he knew it was for the best. Especially since Keiki was still traveling to learn new things.

I know you are probably going to hate me for saying this but...where is Itachi's girlfriend? Even though she isn't talked a lot about in the anime he did have a girlfriend before the massacre. He had to kill her obviously but this is before the massacre so where is she? A lot of people forget about his girlfriend but she is considered a canon character. So what happens between them? Do they break up and he meets Keiki? Or does Keiki meet and catch Itachi's feelings before the Uchiha girlfriend does?

Relationship With Canon Characters:
Uchiha Itachi - Keiki and Itachi met when the two were both doing a mission in the same village, and they were both curious about the other, especially Itachi since he wanted to find out more about Keiki and why he defected. Throughout the months of being together, Keiki fell in love with Itachi, while Itachi himself was left conflicted if he loved him or not. After Itachi left back to Konohagakure, he found out that he did love Keiki back, thanks to Shisui's help, and he was upset he could never make it clear to the other at the time. Throughout the years of Naruto/Naruto Shippuden, Keiki practically being invisible, Itachi meets Keiki once again as a reanimated shinobi, which makes Keiki burst into tears at seeing the one he loved dead yet forced back alive. After managing to calm him down, Itachi told Keiki everything, which made Keiki even more upset yet happy that Itachi trusted him enough to know these things. In the end, before Itachi left to go do the thing with Kabuto, Keiki kissed Itachi (lovingly/passionately) who returned the kiss. Once that was finished, Itachi left with their final goodbye.

Cute but remember that itachi left after the fight with kabuto so Sasuke would be there and it was to stop Kabuto. This part of the anime is very important and shouldn't be changed. However, I would recommend making a different happy ending but still a happy ending with them together. Only reason cause that scene was one of the only sasuke and Itachi moments seen in the show.

Other:
Keiki is pansexual, like my other character Tsubasa, and he died in the end of the war when he protected Sasuke, who he has been watching over secretly since Itachi left once again. Sadly, only the Kirigakure knew who he was, but refused to do anything because of him being a S-rank missing-nin of theirs. So, he died forgotten and alone. But don't worry, in the end, he became happy, as he is now with Itachi and his family somewhere.

Now this is a beautiful and happy ending where itachi and Keiki end up together. It's perfect. Also great job making a OC of a different sexuality, it's cool and unique.
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Well guys what I have to say will be in the next review. For now let's do the final analysis.

Final Analysis- This OC is amazing and has little to nothing to work on. The only things that need attention is the relations to Itachi and the girlfriend also the interference with the Sasuke and Itachi moment that if didn't happen he wouldn't have disappeared because he did it. Remember if Itachi didn't do his jutsu against Kabuto than he and the others that got reanimated wouldn't have disappeared at the end. It is a very important scene in Naruto. There was also some questions that needed to be answered but other than that this OC is amazing is a extremely unique. Thank you so much for letting me review him. It was a honor.