Twelve-year-old Mars, the first prince of the kingdom of Farune, lives in constant fear of assassination. Nearly every meal prepared in the castle is laced with poison, forcing him to sneak out into the monster-infested forest beyond the walls to hunt and cook whatever creatures he can find. The meat is revolting and difficult to stomach, but it keeps him alive. One night, while searching for his next meal, a red-haired woman carrying a massive greatsword appears before him and declares that he has promise and must become her apprentice. Mars is baffled by her insistence, but the woman—Cassandra, a legendary sword saint—has recognized something he does not yet understand: eating monster flesh grants the consumer strength. What would kill an ordinary person instead makes Mars grow more powerful with every bite.

Under Cassandra’s brutal three-year training regimen, Mars develops combat abilities that far surpass ordinary human limits. He also begins to absorb unique traits from the monsters he consumes, gaining not only sword skills but even the ability to wield magic. As his strength increases, he attracts a growing circle of loyal followers whose devotion is so intense that they begin to act on his behalf without his approval. A cascade of misunderstandings transforms the reluctant boy into a figure his allies and enemies alike believe to be an ambitious and terrifying conqueror. Where he sees simple survival, others see a ruthless king who crushed the nobility, seized the throne, and now sets his sights on the entire continent.

The story expands from a personal struggle against poison and betrayal into a continent-spanning tapestry of wars, political intrigue, and escalating conflicts. Mars faces hostile nations such as the warlike Ronza Empire, whose soldiers also consume monster meat but with far more aggressive intentions. He contends with the great religious authority of the Marve Church, which declares the eating of monster meat a heresy and forces his kingdom into confrontation. Along the way, new allies and potential brides are drawn into his orbit, including the fierce warrior princess Carmilla and the elegant saint candidate Maria, each adding to the political complexity Mars never wanted. Despite his desire for a quiet life, Mars is repeatedly dragged into massive battles, strategic negotiations, and even a second royal bride selection meeting, all while the truth of his reluctant nature remains known only to those closest to him.