[His eyes are darting back and forth between Yuu and Zero - though he finds he can't actually look straight at his friend. The other boy will blame himself, he knows that.
Then suddenly there's another person and of course he thinks that she too must be a hunter if she knows the one already in front of them. This is it, he's dead. They've come to kill him. Mika takes another step away from Yuu even as the girl scolds the man.
Now he isn't letting the two of them out of his sight. It isn't that he wants to die now that he's been reunited with Yuu but he doesn't want them to think that Yuu is a vampire too.
Honestly it's a little hard to believe that they're both trying to help. Mika doesn't even know for sure if the lady is a vampire hunter too but he knows for sure the man in.]
You're a vampire hunter, you hunt vampires.... [His fists grab at the orange jumpsuit.] I'm a vampire.
But you can't hurt Yuu-chan! He isn't-- [Hiccup] a vampire too!