Isafuyu is the daughter of the priest of the Mapputatsu Temple.

Isafuyu has a shy personality. She is first introduced when Grandpa Kunieda takes Oga and the others to spend a night at the Mapputatsu Temple. She immediately recognises Baby Beel's true nature and is greatly scared of him. Kunieda requests her help to learn how to fight against demons in order to fight the 34th Pillar Squad along with Oga and Tojou.

In order to help Kunieda, Isafuyu takes her to see Koma, a demon who lives near the Mapputatsu Shrine.

Isafuyu is spiritually aware and can can tell whether a person is a demon just by looking at them. She was able to tell that Baby Beel was a demon and a very strong one. Other than demons, she can also detect the presence of ghosts and can also perfrom exorcisms on demons and ghosts. She was assisted by Koma is fighting demons.

(Source: Beelzebub Wiki)