Birth date: September 7
Sayo Hirasaka is a second year student at Sakurazuka High, and member of the Gardening Club. In the anime, she is introduced in a round-about way. She is seen with her parents during the incident with Ryouichi Karasu—the demon crow destroys the highway the Hirasaka family is driving on, and smashes their car. It is assumed the innocent Sayo is killed in the crash, much to Tatsuma Hiyuu's grief.
SpoilerSayo returns later on, surprising Tatsuma by running into him by coincidence. The two seem to start dating, which shocks his friends; Kyouichi is the only one to remember the girl, causing him to be suspicious. Because her parents were killed, Sayo claims she must leave Tokyo for the countryside, to live with her grandparents on a farm that cultivates sweetpea flowers. Tatsuma accompanies her on the train ride, and walks her to her grandparents.
However, he falls into a trap by Tendou Kodzunu. Sayo had indeed died with her parents, but was resurrected by Tendou's Dark Arts; the half-dead corpse of Sayo accepted his offer in exchange for also bringing back to life her parents. In the end though, she couldn't stand betraying Tatsuma and saves him—only to be stripped of the power keeping her alive.
Sayo's history is slightly different in the original video game, but she is still used the same. She is also a descendant of Hirasaka from the prequel game Tokyo Majin Gakuen: Gehouchou.
(Source: Wikipedia, original video game data)