I Kept Pressing the 100-Million-Year Button and Came Out on Top Novel Vol.1 (US)

Allen is training to be a swordsman, but he’s just no good at it. After losing a duel with high stakes, he’s about to drop out when a mysterious man offers him a chance to get 100 million years’ worth of training with the press of a button. But what happens when he presses it over and over?!