wow, I might be remembering wrong but it sounds like they changed a lot in the light novel version. I think the god of undeath was originally a yandere goddess in the web novel who made people undead out of pity. She had a crush on him. The god he followed was her sister, the goddess of death. He gained the power to free the undead and used it on his parents before going on a journey to free others. Basically, the whole circumstances surrounding him where completely different.
tl;dr
THEY CHANGED A FUCKTON