Tsuyokute New Saga

The Demon King led his army of demons to wipe out the human race. The Hero, Kail, and his allies attack the Demon King's castle to defeat the Demon King. The Demon King is slain, but at what cost? Kail lost all of his allies throughout the war. Friends, family, lovers, comrades. All dead. As he lay dying at the foot of the Demon King's chamber, he notices a strange gem that the Demon King had coveted and approaches this relic to grab it, after intense light glows, he is sent years into the past. After recovering from the initial shock, now in his younger body he decides to use this opportunity to avoid making the same mistakes of the past and become stronger.