In a world where innate skills determine one's destiny, Fate Graphine lives a bleak existence as a gatekeeper, burdened by the supposedly disadvantageous skill of Gluttony that constantly drives his hunger. He suffers abuse from the holy knights, who are meant to protect the people but view him as a liability because of his skill. Fate's perspective changes dramatically when he kills an escaping wounded thief, and unexpectedly, Gluttony activates, enhancing his abilities and stats.
Inspired by this newfound power, Fate accepts an offer from Roxy Hart, the only compassionate holy knight in the area, to join her team. Determined to explore the full potential of Gluttony, he allies with a mysterious sentient sword named Greed, who warns that Gluttony is an illicit skill that disrupts the world's natural balance. As a result, Fate must now lead a dual life, hunting monsters nightly to appease his awakened craving for souls, or face the danger of losing control and jeopardizing any hope for a better life.