Sena Yuu

Suzuki's roommate and friend since junior high school. She and Suzuhime work together at “Shiro no Koshika-tei”.

Despite her fearless appearance, she has a serious and simple personality. She is not good at improvising. She struggles to stop Suzuki's outbursts, but her efforts usually end in vain.

She is also a member of the same swimming club as Natsumi, and Natsumi is a senior whom Yuu admires. She is also active in the school's general security club, but does not remember having applied to join the club. As she says "While hanging out with Suzuki, before I knew it, I became a member."