Boushokuki no Ken

After Dean, a third rate adventurer, got surrounded by demonic beasts in the demonic labyrinth, he fled to a place where he found the strongest demon who devours power: the demon-fed sword Belzera, born to the Gluttony Empress Belzebuth. After obtaining such unexpected power, he once again aims to become a first rate adventurer he looked up to, and delves deeper into the labyrinth. However... (Source: Overlap, translated)