Previously

Percy gets roped into helping Leo with a Monster which has been following him. Since Leo saved him from a crowd, they bonded and now Percy feels the need to repay him. He also feels pity for Leo since he reminded him of his own unfortunate past. 

Percy also gets excited since it would be the first time after returning from the House of Wolves he would be fighting a proper Monster. He wants to test himself and hopes the monster following Leo is strong enough not to be an annoyance. 

***

Till now Leo had only one game plan in mind. When it came to fight or flight, always choose flight. It was a fine strategy, if he said so himself, but it was the complete opposite of what he was doing.

Now to ask what he was doing- he was following Percy as they hunted down the very monster which had been hunting him.
Yep, they were running towards the exact same thing which he had been running away from.
Lovely.

Percy had swiftly asked Keria to scout from the air and within minutes, she ready to guide them, filling him with newfound dread. He had desperately prayed that the damn bird would get caught up with clouds or something. 

He had no idea it was so close to him. He'd had a few close calls with that 'thing', but he'd been extremely careful and sneaky. At least, he'd thought so.
He shuffled his feet in nervousness, suddenly feeling very grateful that Percy was with him. Heck, he even felt grateful to the terrifying presence of Keria as the flap of her wings resonated closer.

Leo kept behind Percy, his years of 'not-staying-still-in-a-place' allowing him the stamina to keep up with him. There weren't particularly in a rush, but they wanted to be away from as many people as they could, or so Percy said. 

As they went on to the outskirts, Leo noticed that Percy was constantly doing something. It began with subtle movements, things like digging around his waist and scratching his leg but slowly, he realized that if he focused, Percy was doing much more than that. 

Suddenly, 'digging around his waist' had turned into drawing out KNIVES (!?) and rubbing his leg gave birth to thin needles? He was right behind him but had no idea what was in Percy's hands. He suspect the 'veil' was blurring things for him. It gave a delirious experience.

Before he could get a better look at his weapons, Percy reached up and removed the tie holding his hair. It tumbled down, wavy but in weird shapes. He must've kept them bound for a long time. His hair was much longer than it initially appeared. 

All the while Leo had known him, his hair had been haphazardly held up, in something like a updo, with strands coming out here and there. He had known it was longer than the average young boys he saw, but now that it was loose, it brushed his shoulder blades as the wind whipped them. 

But just as soon as he freed them, he pulled them back taunt and tied them tight. 
For the fight, Leo realized. He reached up and patted his curly bush, thankful for its short length. 

Now that there were no bits framing his face and softening his eyes, Percy looked as intense as he could be. His face were hard lines and determination, no hint of a smile.  

Looking at how Percy was readying himself, Leo also did his best to copy. He tucked in his shirt, shoving in the loose ends and glanced down to check his laces. It immediately gave him something to focus on other than the racing of the heart. 

While Leo was finally calming down, Percy had started getting anxious. 

Keria had already hinted at the monster. And it was times like these where Percy wished Keria would just 'tell' him. He had a pretty good idea about what was coming and he was damn well excited about it too. 

The only problem was that Percy was a solo player. He preferred hunting alone and protecting someone was not a strong suit of his. The only experience he'd had with other people included them having some knowledge about monsters and fights. The times he'd 'protected' were animals and they had honed survival instincts on which he heavily relied. 

Leo had no knowledge about monsters and nor was he an animal. 

Nevertheless, Percy kept on going forward, his mind trying to conjure up as many strategies and worse-case-scenarios as possible. While he was furiously thinking, his body went on autopilot, going through his pre-fight routine. 

Check the knives, get the poison on the needles, have his arm covering ready for Keria, make sure his clothes were not flabby and so on. It wasn't necessary since he had Riptide just a thought away, but again, he was always going to be prepared for the worse. 

His senses were on high alert. The moment it came near, Percy would know. The Nature would tell him. The Spirits were happy to help. Just having Percy in their territory made them stronger; such was the power Pan gave him. 

And it wasn't long before Percy knew. 
"Stay quiet." Percy swiftly grabbed Leo's arm and crouched behind a sort of shack. A bus stop, he noticed once he read the sign. Might be abandoned. It was old and creaky and left rust stains on their hands. 

"Stay hidden. Don't make noise. Keep your breathing even and if the situation calls for it, use your wits but DON'T rush in. Got it?" Percy rattled off quickly, murmuring low. "Stay alive." 

He looked right into Leo's eyes which had buried the mischievous sparkle. He was used to seeing such reservation. Jason, Reyna, Luke, Annabeth, Thalia, all of them being kids which had learnt to stop acting like one. 

But it wasn't time for lamentation now. He gave a quick squeeze to Leo's hand and ran from the shack, hearing a bone rattling roar which was unique to only one monster.

"MOOOOO"