Paladin of the End

Paladin of the End summary:

A town ruined because of deaths. A child and three undead exist there. The three undead who used to be heroes raised the young boy, Will. Giving him skills, giving him knowledge, pouring all their love into him, the young man was raised that way. He was told about the mystery embraced by the undead, about this hidden town of death. After learning all this, this youth started to walk on the path of the paladin.