Although the Dark Axe gives almost enough +ATK to shred through the first two bosses right away, its horrible scaling prevents it from being useful beyond the first few battles. It is however found quite early on, which makes farming for it rather straightforward and worthwhile, except if you somehow manage to get your hands on a Mace or a Samurai Long Sword for some reason.
In-game stats Edit
Cost: Can't be bought
Category, ID: 0,22
Drops from: Red Demon Axeman (looks like some sort of caterpillar) @ LV 4170, Graveyard zone