Ichiokunen Button wo Rendashita Ore wa, Kizuitara Saikyou ni Natteita: Rakudai Kenshi no Gakuin Musou

On the verge of flunking out of Grand Swordcraft Academy due to his total lack of talent, Allen Rodol’s life goes from bad to worse when the class prodigy challenges him to a duel where it’s win or face expulsion. However, the night before his hopeless bout, a mysterious hermit grants Allen a button that will give him one hundred million years to train in an alternate reality when pressed. Allen not only gladly accepts the offer but also goes back for seconds, thirds, tenths even! With over a billion years of straight practice under his belt, the world is about to see what the “Reject Swordsman” can really do!

(Source: Yen Press)