A squad of thirteen heroes sent to slay the Lord of Dark Beasts, Clevatess, is utterly annihilated. Enraged by this attack on his territory, Clevatess marches on the human capital of Hiden, leaving a trail of death and destruction. As he stands amidst the smoldering ruins, a dying woman makes a final plea for him to spare a single newborn infant. In a decision that defies all expectation, the demon king agrees and decides to raise the child himself. To care for the baby, he resurrects one of the heroes he just killed, a young woman named Alicia Glenfall, binding her to his service. The infant, named Luna, becomes the unlikely last hope for humanity, as Clevatess declares he will judge the worth of the human race based on her development.

The story follows this strange and uneasy family. Clevatess, a horned, fox-like beast of immense power, disguises himself as a quiet human boy named Clen to travel the world. Alicia, a skilled warrior now scarred both physically and emotionally by her death and unwilling resurrection, is forced to act as the protector of the very being who killed her. Their relationship is a jagged, dependent partnership, filled with mistrust and philosophical clashes as the demon lord views human morality with cold, anthropological curiosity while the former hero clings to her sense of right and wrong. Their journey to find a wet nurse for Luna leads them to a bandit camp known as the Ravens, where they encounter Nelluru, a young slave woman who has suffered a lifetime of brutal abuse. Recognizing her innate kindness, Clen and Alicia rescue her, and Nelluru joins them as Luna's devoted caretaker, finding a new purpose and a second chance at life.

The setting is a dark fantasy world where five humanoid races are constantly at war with the armies of the four Demon Beast Kings. The kingdom of Hiden, left defenseless after Clevatess's attack, becomes a target for neighboring nations eager to seize its legendary forge, a facility that creates the powerful weapons used by heroes. As the group travels, they uncover the grim truths behind their world's power structures. A significant narrative arc involves the revelation of the Hiden Forge's true nature: a brutal mechanism that manufactures kings and heroes through sacrifice and secrecy, exposing the myths of legitimacy and destiny that society is built upon. Alicia, once a wide-eyed adventurer, is forced to confront the deep-seated corruption beneath her kingdom's traditions.

The first season consists of 12 episodes that chart the group's struggle for survival and their growing, if reluctant, bond. After the intense opening that establishes the core premise, the story follows their fight to free Nelluru from the bandits, an arc noted for its unflinching depiction of slavery and abuse. The middle portion of the season delves into the wider political conspiracies of the world, at times losing focus on the central trio. However, the narrative regains its momentum in the final episodes, leading to shocking revelations about the true origin of the hero tradition and a satisfying conclusion that sets the stage for a second season. The season ends with the found family more tightly bound than ever, having survived not only external enemies but also the dark secrets of their own world.