Jinko Sasajima

The younger sister of Buzou High School Quiz Club Captain Gakuto Sasajima. Although people notice they don't look alike enough to be siblings.

She was first introduced as the mystery girl riding on Gakuto's bicycle on the way to school. Then, she met Shiki in his usual spot in the library. Weakened by hunger, Shiki shared his food with her.

It is implied that she is into electronics, as she had unknowingly left an Electronics book with Shiki on the first time they met. Shiki and Daisuke find it "moe" due to the fact that "cute girls buying electronics at the Akihabara district" are rather rare.

As such, it is implied that she is learning how to make buzzers at a cheaper cost since they're usually expensive.