Koinui Mutsuki was on a date with Nanami, a classmate that she is in love with, when he confessed to her. But soon after confessing, he died in a sudden accident and while she was still reeling from the shock, a grim reaper suddenly appeared in front of her. The grim reaper then offered to send her back in time to save Nanami in exchange for a few years of her life. There are two conditions for Nanami's death and they are: "when Nanami confesses to Mutsuki" and "in second year of high school". Will Mutsuki be able to successfully avoid Nanami's confession and save his life? source: https://www.mangaupdates.com/series/iquwnyz/gomen-nanami-kun-to-wa-tsukiaenai