Koizumi is probably unhappy that his girlfriend seems to be infatuated with the mysterious new member of the club.
Asahina-senpai!Then what if I were to call you "Asahina-senpai"Eeee♡Please show me how to make tea!Eeee♡You seem awfully enthusiastic about helping her.But she's so cute!And when she calls me "Asahina-senpai" it just makes me want to do whatever she asks♥Would you let me do anything I wanted?Not me doing it, but you doing it?