Tail of Rot to Steel

[Also uploaded to Royal Road, same username as the one here.] Everyone in class received a divine gift. Kazuya, the guy who stole my childhood friend and made my life hell, was crowned SSS-rank Hero by the gods themselves. Me? They branded me F-rank trash and abandoned me in the world's strongest dungeon to die. No hidden power awakened. No goddess took pity. No system glitch turned me into a secret overlord. Just a discarded weakling. and the monster I'm prepared to become to drag that "Hero" down from his throne. [Can a tail of rot, turn to steel?] — Description from novelcodex.org