Koko wa Ore ni Makasete Saki ni Ike to Itte kara 10-nen ga Tattara Densetsu ni Natteita.

When the Hero’s party is ambushed by an overwhelming horde of powerful devils, total annihilation seems inevitable. To save his companions, Rakku, the group's strongest mage, makes a desperate decision to hold the line alone. Promising his hesitant allies that he will catch up shortly, he urges them to flee while he faces the enemy. What follows is not a brief skirmish, but a relentless, decade-long war. Utilizing his unique skill, Learning, Rakku continuously masters the devils' magic as they attack. By absorbing their vitality through abilities like Drain Touch, he fights without rest or sleep for ten years, growing stronger with every encounter until no enemies remain. Upon finally returning to the capital, Rakku discovers a world transformed by his absence. He has become a living legend—his name now serves as currency, and a towering, idealized statue stands in his honor. Furthermore, the constant absorption of demonic life force has reversed his aging, leaving him with godly powers and a youthful appearance entirely unfitting for his true age. Realizing he stands out far too much, Rakku decides to conceal his identity. Disguising himself as a novice F-rank warrior rather than the S-rank mage he truly is, he sets out on a new adventure in a world that is supposedly at peace.