I Became a Legend After My 10 Year-Long Last Stand

ここは俺に任せて先に行けと言ってから10年がたったら伝説になっていた。

Sorcerer Luck Lock Franzen holds the line alone against the Majin army so his companions can escape, expecting the stand to be his last. He wins. By the time the battle actually ends, though, ten years have passed, his body has reverted to that of a teenager, and the world already remembers him as a legendary Great Sage. Rather than step into the myth built around his name, Luck fakes a new identity and signs on as a rookie with an ordinary adventuring party, trying to disappear into an unremarkable life his own reputation won't let him have.