Kotomine Kirei

Through an agreement between the Mages' Association and the Church, the Holy Grail Wars are moderated by a priest. Kirei's father was the mediator for the fourth Holy Grail War, and when he died, Kirei felt obligated to replace him. His selection as a mediator is unusual, for Kirei is a member of both the Church and Mages' Association, organizations on hostile terms with one another.

Since the death of Rin's father, he has acted as an indirect caretaker for Rin.

Spoiler

Ranked far lower in the Church hierarchy than Ciel (from Tsukihime), Kirei employs many of the same techniques and weapons she does.

He is surprisingly convincing as a magus, having trained under Rin's father.