Cycle of Carnations

After a horrific incident leaves a young man dead, he is greeted in a space between life and death by a magical girl named Rein. Rein introduces herself as something of a guardian of reincarnation, but when deadly occurrences continue on into his next life, he has to wonder: who is Rein exactly? And what connection, if any, does she have to the cyclical violence that he seems trapped in?