18+ Ore dake Haireru Kakushi Dungeon: Kossori Kitaete Sekai Saikyou

Noir Stardia, lesser son of an even lesser noble, just lost his job. Without a penny to his name, he decides to enroll in the Hero Academy and improve his career prospects. But he’ll need to get a lot stronger to pass the entrance exam. So Noir seeks out a hidden dungeon—a legendary labyrinth filled with strange beasts and rare items—where he can train until he’s powerful enough to change his fate!

(Source: Seven Seas Entertainment)