I forgot if it was Japanese or Chinese. It was set in a sword and magic era, likely western medieval. It was about a boy who liked a girl, said girl will be married to a slightly older adventurer/hero of her father's sword school. I think she was going to a city to be educated. Before she does the boy ran away, the family is heartbroken and the adventurer promises to help find the boy. However the boy dies and emerges in hell as a bottom rung demon. He manages to gather a bunch of lowly demons and through killing other demons evolve. While others become powerful he evolves into a succubus which attracts more demons. He leads his band up the sinking tower absorbing and eating other low demons and passes into the next level, a barren wasteland. There is harpy and a maze of some sort on this level and after passing through to the next level he was forcibly summoned into the human world. He kills his summoners and befriends a few of the captive girls (the cult was using them as demon summoning meat material). One was a silent thief. They kept one of the cultist alive but severely disfigured and mutilated and they were about to head out to a city in a wagon. The rest of the prisoners decide to go home.