Watashi no Kizu wa Shinde mo Kesanai

The manga centers on Yamaneko Nokishita, a boy with two childhood friends. The first is an older college girl who has a scar on her forehead that Yamaneko is connected to, and swore that he would "take responsibility forever." The second is a classmate, the diminuitive Mameshiba. The three sometimes hung out together, but when Yamaneko entered his third year of high school, an incident happens when he visits Mameshiba at home...

(Source: Anime News Network)