After nearly a century of war against the demons, humanity finally seized victory—but it came at the cost of countless lives. Zavier, humanity's last warrior, breathed his final breath filled with regret for failing to save his comrades and burning hatred for the Demon King—or so it should have been. However, when he opened his eyes, the very scene of his birth lay before him! Blessed with a talent for magic he never possessed in his previous life, Zavier vows to become a Magic Swordsman, gain true strength, and exact his revenge this time around. One day, while training in secret, a twist of fate causes Zavier to fall into the legendary "Abyss." Waiting for him there was the World Tree, plagued by a mysterious disease, and the Goddess who guards its roots. Can he unravel the truth of the world and protect those he holds dear from the demons? The battle for humanity's future begins now!