Itsuki Yamagami 山神異月

Takamasa's Shikabane Hime. She died in an automobile accident and came back with the regret of not living the life of a teenage girl. She bonded with Takamasa because she thought he was a powerful monk and would help her get to Heaven faster. Unfortunately, Takamasa knew nothing about the Shikabane Himes before that. Regardless, the two continued to work as a team. Source: Wikipedia