Hidamari no Kioku

Tatsuya Kinoshita quit going to school because of a bully.
He became a fragile shut-in (hikikomori) who might never get past the damage.
The only person that gave him a reason to keep living was Hinata, a girl he knew his knew his whole life,
and the only one who treated him like a true friend before and after the bullying.
But she gave her heart to the bully that drove him to this life...

[from DLsite English]