Chishiya expected the possibility of others trying to assault him, now that the rules of the civilized world are gone. However, what he couldn't predict was the fact that someone would steal his hoodie from him, of all things.
He remembers you from before. He was a medical student on practice, appearing to be all lovely and polite on the surface. It's what society requires—it was simply logical to play this role in order to get what he wants. To say it shortly, he wasn't a good man, but he was a likable man, an adaptive machine, all thanks to that brain of his. He does what he should to survive. Now, in Borderlands, as it is called by many, there are other methods of survival. It's much more primal, much brutal, and his actions, naturally, correspond.
You saw his ruthlessness. He wasn't sadistic, like some people you see among Beach members. He was indifferent, which, perhaps, was even worse. He doesn't flinch when the blood splatters nearby. He doesn't cry or panic when he's on the verge of dying. He keeps a straight face, and once he wins, like he always does, he only smirks because he knows that there's no way he wouldn't be on top anymore. He was, and he always will be. He's not overconfident—he knows what he's made of and who he is. And what he is smarter than everyone else who surrounds him, and he will be the first to get out of his hellhole, no matter how much he will be called bastard for stepping over others' heads for his goal.
That's why you like him, don't you?
Surprisingly, he was feeling more amused than irritated. He took his sweet time before actually confronting you. He bets there was not a single moment when he was oblivious to you watching him, and it was pretty cute, from his point of view, how you desperately attempted to hide. He hopes you realized that if he's intelligent, he's also observant enough to catch you. But not like he ever gave you anything but brief clues about him recognizing you. He felt, in a way, like a performer on the stage who doesn't have a scenario to talk with the public. Although it's less entertaining, it's better at giving you illusions, at fully committing yourself to the story.
He wondered how long it would take you to do something more. It wasn't difficult to untangle your plan—he saw through it the moment he smelled the unusual freshness on his hoodie. Apparently, you somehow sneaked into his room, stealing his favorite item to wear that he was so easily recognized by, and instead replaced it with another, identical one, certainly taken from the abandoned clothes store, assuming he would be dumb enough not to catch the faintest difference. The copy was a bit clearer, a bit newer, like any new unused object. Well, he can't blame you for trying. No matter what you would've tried, he'd figure it out anyway.
Night, Beach. Those who can appreciate breathing another day are currently partying in all the canons of this place, yet you're currently returning to your designated room. The hoodie, soaked with Chishiya's presence in a metaphorical sense as it is in physical too, is plastered on your bed. You start to nuzzle into it, committing it into memory; however, you can't relax for too long—
"My, seriously?" Chishiya scoffs. He didn't even need to come up with a good disguise or search for a special spot to appear like a ghost. His hands rest in (not really) his hoodie pockets as he casually leans against the wall, glaring down at you.
"Should I steal something from you, too, to make it even? Or, no, you would enjoy it too much, wouldn't you, little thief?"