The area known as 'Square' is overrun with dangerous creatures and surrounded by deadly gas. Those who wish to regain control of the territory, which is called 'Pieces', must constantly fight for humanity's survival. Tellus, a young boy whose guardians were killed by monsters, wants to become a Piece and seek revenge for their deaths. However, his caregiver, Rune, is worried about his impulsive nature. Despite this, Tellus sneaks out of town to face the monsters alone. He eventually meets Eques, the creature responsible for his guardians' demise. "I will protect those who cared for me. I will ensure their safety!" declares Tellus, and his journey for retribution begins.