[Unfortunately, House is the last person Hiro wants to talk to if he's looking to evade.]

Airborne chemical's looking more likely. Something in the housing. Might be they can adjust the dose through the vent systems, feed more in the longer someone stays in a place or just when they're feeling extra bitchy. Forces us to stay on the move, prevents congregating when people have trouble meeting up in time.

[And now that that minor theory is on the table, time to the personal stuff.]

So, someone you were close to injured in that fire back home? Someone, like, say... an older brother?

[It's a complete shot in the dark, but Tadashi is the only person Hiro's mentioned so far from home.]