ORE NO BUKI WA SAIJAKU DAKEDO LEVEL UP SURU RASHII

I, a NEET, turn my life around from one of constant oppression to become the mightiest hero—and the secret lies in… a battered, broken “weakest weapon”?! It was the only weapon in this world with the ability to level up. This is the story of how a protagonist, once mocked as a failure, becomes a hero who saves the world alongside the weakest weapon! (Source: Ganma!, translated) Note: Includes one extra chapter. — Description from AniList community (anilist.co).