Shiki Tohno's former classmate and fellow badminton club member from junior high.

During the winter vacation of her eighth grade year, Yumizuka had found herself stuck in an old warehouse during the winter. Shiki ended up saving him, leading to Yumizuka falling for him.

In her non-existent route, she had her blood sucked out by Roa, which turned her into a vampire.

Because of her innate spiritual nature, she was able to become a bloodsucker immediately after his death and escape from Roa's control. Even after she had just become a vampire, she still had the memories and knowledge of her human life, which indicates that she had exceptional spiritual qualities.