The blond narrows his eyes, muscles immediately tensing and readying to either defend or counter, just on sheer reflex, daring the thing to try it. Obviously, it does not, and Katsuki only loosens the tightness in his shoulders a tiny bit...eyes still on the mech. Whatever this guy is doing to it is working like a fucking charm, but he's still not exactly about to trust either of them. The mech...and then the one keeping it passive are both dangerous in their own right.

"Bios..." he clicks his tongue, thoughtfully. "That's like this place's energy, isn't it?" He still doesn't quite understand the concept too much, honestly. Is it kind of like, ah...mana? Like the stuff you hear about in an RPG? Life force??

"You say that stuff is powering these things? So in a way, they're...alive?" He doesn't like that. It means he has some sort of...ethical dilemma to think about now when he takes them out. Blech. "...What're you even going to do with the information you're gathering?"