If there was anything Inumaki Toge prided himself on, it was his observantness. So when Yuuta didn't show up for class, Toge was the first to notice. (Or: The one where Yuuta relapses into his self isolation habits, and Toge doesn't know why, but Gojo might have some insight along with a request.)

Toge being in one of his various calming elements wasn't what stood out to him the most. Toge was singing.