He might need it one day, huh...? That's not something a possible betrayer says to the person they plan to betray. At least, in most cases it's not, as far as he knows. Maybe it's just a trick, and she has a second name that she doesn't plan on telling him... Chikusa wishes he didn't have to think about such possibilities, but, still. Ayumu has reminded him of how carefully he has to.

...Well. He supposes there's one other reason someone could tell another their vessel name. But Chikusa won't ask about that.

Instead, he blinks at her for a moment before lazily pointing just one figure and deadpanning, "Shuuki, Silence."

He's not actually trying to cast; there's no will behind it.