I Kept Pressing the 100-Million-Year Button and Came Out on Top, Vol. 1 (light novel)

Allen is training to be a swordsman, but he's just no good at it. Afterlosing a duel with
high stakes, he's about to drop out when a mysterious manoffers him a chance to get
100 million years' worth of training with thepress of a button. But what happens when
he presses it over andover?!