After a century of conflict with the demons, humanity finally achieved victory, but the cost was enormous. Xavier, the last surviving warrior, died filled with regret for failing to save his comrades. Yet when he opened his eyes, he found himself reliving the day he was born and he had even gained magical talent he never possessed in his previous life. Determined to grow stronger and carry out his revenge, he trained in secret, only to fall by chance into the legendary Abyss. There he encountered a World Tree afflicted by a mysterious illness and the goddess who guarded its roots. As he uncovers the truth behind the world, Xavier steps into a new battle to protect those he holds dear from the threat of the demons.