The protagonist, along with his stepmother and two step-aunts, is summoned to another world where demi-humans reign supreme. However, they are not called upon to fight a demon lord, but rather to combat the Undead Apocalypse—hordes of monstrous beings known as “Dead Mell” that have overrun the land. These creatures can only be slain using weapons forged from holy silver.
To face this threat, they must form a battle unit—a four-person family—each assuming a crucial role. The swordmaster wields the holy sword, the guardian commands the power of the earth to defend, the healer harnesses the power of water to restore, and the black mage manipulates fire to annihilate. Among them, only the swordmaster can vanquish the Dead Mell, while the others provide essential support.
However, using magic comes at a steep cost. To forge a contract with spirits and access their powers, one must offer a piece of themselves in sacrifice—the greater the sacrifice, the stronger the magic. Now, they face a difficult decision: which three will relinquish part of their bodies to gain power, and who will take up the sacred sword to lead the charge?