Ichiokunen Button wo Rendashita Ore wa, Kizuitara Saikyou ni Natteita: Rakudai Kenshi no Gakuin Musou
There was a mysterious old man who approached the failed swordsman with the “100 million years button”. A magic button which can achieve the same effect as training for 100,000,000 years if you push it. The failed swordsman who pushed the button had his doubts, but immediately felt tremendous power rising in his body. So he pushed the button many times. However it was a cursed button. The moment it was pushed, he was confined to the 100 million years prison of time. The first 100 years were devoted solely to training. After 1000 years he had forgotten why he swung his sword. He stopped thinking completely after 10,000 years had passed. After 100,000,000 years he became crippled and finally managed to return to the real world.