Tsuyokute New Saga

The Demon King led his army of demons to wipe out the human race. The Hero, Kail, and his allies attack to 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.