The Underworld Transcendent Returns

Leon Klein, the Grand Mage who defeated the Demon Lord and saved the world, falls into a dark pit after Prince Schalk attacks him and reveals that he’s burned down the orphanage Leon cares deeply about. Trapped in the abyss, Leon spends the next decade slaying endless hordes of monsters, acquiring mysterious spells, fueled by his desire for revenge. Leon finally escapes this hell, only to wake up in the body of Ren Kuroba, a bullied teenager who attends the prestigious Seio Academy. As he adjusts to his new life, Leon soon discovers that Schalk is also here, advancing his sinister plans behind the scenes. Leon may have a new identity, but his quest for vengeance is far from over.

(Source: WEBTOON)