Man, Okita has a hard time with camp vampires, and people who can tell he's not human. He hasn't been like he is THAT long, he's not really used to thinking about himself that way and not trying to, but he's also spent a LOT of time thinking that the rasetsu need to be kept a secret. So when people ping on him, his instinct is to not like it. And possibly to pick a fight.

However, he's not that dumb, and he can tell something is wrong. And under the circumstances, he does sympathize with Zero's caution and suspicion. He's got some idea how bad things could be getting, and Zero was... not unhelpful. So his impression over all was of being on the same side! Even though he's prickly about being known for something vampire-like.

I have an idea, but again the reverse. XD