It does Counterattack. In Nutaku terminology, that means "the lower HP = the more damage you gain from the buff"
You're probably mixing it up with Intercept.They don't reset. But don't waste it on Gaia's weapon. Bricks are best used on SSR Hime weapons that either gain a third skill from their FLB or a second Assault.... no. A brick is a thousand times better, don't even consider the waste of perfectly good Medals on effectively nothing. Yes, you might not have anything to even brick right now, but you'll be thankful when after two more Towers you've found a good FLB Hime weapon and have your bricks ready.