A boy, Allen-Lordle, was despired by his classmates at the sword-arts school for being weak. He was challenged to a duel by the strongest swordsman in his year to quit the school if he lost. Despairing, he wandered into the forest where an old man offered him a "100 million year old" button, pressing it would enable him to train for 100 million years in a pocket dimension.
Allen pressed the button, obtained amazing sword skills, won the duel easily and then obtains a harem.
