Tsuyokute New Saga (LN)

Tsuyokute New Saga (LN) summary:

Kyle and his band of suicide squad head straight into the Demon King’s Castle to put an end to his schemes. With him losing his right arm and leg, he vanquishes the Demon King at the cost of his team and his loved one… Slowly dying as he bled out, he saw a dark crystal in the area, deciding to grab it. A blinding light surrounded him… and somehow he finds himself on a bed in a familiar room.
The Demon King led his army of demons to wipe out the human race. The Hero, Kyle , and his allies attack to Demon King’s castle to defeat the Demon King. The Demon King is slain, but at what cost? Kyle 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.