Umareru Kachi no Nakatta Jibun ga Anna no Tame ni Dekiru Ikutsuka no Koto by Nagase Yousuke — Completed

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Via Myanimelist:

"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.jp)"

Volume 1
Chapter 1 released Sep 29 '14
Chapter 2 released Oct 7 '14
Chapter 3 released Oct 19 '14
Chapter 4 released Oct 29 '14
Chapter 5 released Nov 22 '14
Chapter 6 released Dec 18 '14
Chapter 7 released Jan 20 '15
Volume 2
Chapter 8 released Feb 15 '15
Chapter 9 released Mar 17 '15 Rape
Chapter 10 released Apr 4 '15 Foiled rape attempt
Chapter 11 released May 15 '15
Chapter 12 released Jun 5 '15
Chapter 13 released Jul 19 '15 Rape
Chapter 14 released Jul 24 '15
Volume 3
Chapter 15 released Aug 15 '15
Chapter 16 released Sep 1 '15 Violence
Chapter 17 released Sep 18 '15
Chapter 18 released Sep 25 '15
Chapter 19 released Oct 8 '15
Chapter 20 released Nov 12 '15
Chapter 21 released Nov 12 '15