Osananajimi to no Yakusoku wo Hatasu Tame ni Hyakunen Shugyo Shita Rouyuusha, Nokori no Jumyou de Maou wo UtsuNew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; Demi Menepati Janji kepada Teman Masa Kecilnya, Seorang Pahlawan Tua yang Berlatih Selama Seratus Tahun Menaklukkan Raja Iblis dengan Sisa Umurnya; 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

Berg, whose parents were killed by demons, sets out on a journey to defeat the Demon King. On the night his village was attacked, he promised his childhood friend that he would slay the Demon King. To fulfill that promise, he secluded himself in the mountains and trained relentlessly. One hundred years later, now 110 years old and armed with overwhelmingly powerful punches, Berg finally descends from the mountain. On his way to the Demon King, he encounters Eruruna, an elven swordswoman fighting against the demons...