Ichioku-nen Button wo Renda shita Ore wa, Kizuitara Saikyou ni Natteita: Rakudai Kenshi no Gakuin Musou

Description:
Allen is a boy who is despised as a failed swordsman. One day, desperate for a duel with an elite swordsman who bets on leaving Kenjutsu Academy, a mysterious hermit asks him if he will press the "100 million year button". Can the mysterious object really help him train for 100 million years?...