Hagun Seisenki(1989)

Hagun Seisenki

Year 1691/2:
In a land ruled by the Satomi clan, Inue Shimbē Masashi and his twin younger sister, Fuse, loose their parents—thus becoming the new clan leaders. Inue additionally becomes the leader of the Satomi Hakkenshi as well - 8 elite warriors, loyal to the Satomi clan.

Fuse believes yokai are people, unlike her brother who believes they're merely fiction. After a trip to the woods she is rescued by a yokai named Yatsufusa, who she falls in love with.

Year 1991/2:
The Satomi Hakkenshi have all been reincarnated into people studying or working at CLAMP School. Inue has been reincarnated into a boy named Kazae Tōma, and Yatsufusa reincarnated as a new math teacher named Shirō Fuyukaze.

A battle begins, leaving Kazae’s life is in danger for he cannot remember his past life as Inue Shimbē. It’s up to the Hakkenshi reincarnations to protect him as a quest to break this curse continues on centuries later.