Dokuro wa Yamiyo ni Ugokidasu

An old man with no relatives suddenly has new neighbors. He is touched by the family's kindness, and, momentarily, feels for the first time as if he actually has a family of his own. Until someone murders them. The old man, who has nothing left to lose, turns into a demon of revenge! A story of dark violence! (Source: Shounen Gahousha, translated)