A Gun in a Dungeon

Ashé Crow stumbles upon the City of Agartha, The City with a Dungeon filled with monsters, adventuring is a full-time job, and killing monsters earns you money.

Born with the peculiar trait of natural curiosity and his wits. He is borderline obsessed with creating a weapon that would help him uncover the dark mysteries of the Dungeon itself.

If there's no rules about how to kill the monstrosities that dwell on the bottom pits, then inventing a gun would be a good idea, right?