A successful light novel series-- with a long title I'll abbreviated to WORLD BREAK-- concerned a "magical school" where the students were drafted to fight monsters if they possessed memories of former lives. So far as I can tell from the 12-episode anime series and the one manga chapter available online, the reincarnation angle existed only to give male lead Moroha two immediate girlfriends who can remember him from past (separate) lives. In one life, Shizuno was Moroha's wife, in another, Satsuki was Moroha's sister-- but both modern-day girls want Moroha as a sex-partner.
First, feisty Satsuki:










































