Osananajimi to no Yakusoku wo Hatasu Tame ni Hyakunen Shugyo Shita Rouyuusha, Nokori no Jumyou de Maou wo Utsu

To Fulfill a Promise to His Childhood Friend • the Old Hero Who Trained for a Hundred Years Defeats the Demon King with His Remaining Lifespan • 幼馴染との約束を果たすために百年修行した老勇者、残りの寿命で魔王を討つ