In This World, Falling in Love with You Again

I changed the past, even though it wasn't allowed.Teenager · Shin and the girl he's dating · Asahi suddenly break up.Asahi, who still longs for this love, finds out one day after starting high school that Shin has passed away due to illness.Asahi receives Shin's relic, a "diary", and learns of an astonishing secret hidden within.This secret becomes the key to "revising first love", an unfortunate but also very happy thing.