Umareru Kachi no Nakatta Jibun ga Anna no Tame ni Dekiru Ikutsuka no Koto

A 32-year-old aspiring mangaka, Kazuya Mukai, falls off the rooftop of his old elementary school during a drunken stupor. When he wakes up, he finds himself 20 years in the past, and even his body has regressed to that of a sixth grader. Now that Kazuya has a chance redo his life that had been full of disgrace and humiliation, he hopes to win the heart of a little girl and his first crush, Anna. However, his feelings only lead a whole new tragedy. It's a puppy love that transcends the bounds of time, only to be defiled.

(Source: Amazon)