The protagonist, having died and been reincarnated, wishes to be reborn into a medieval-style fantasy world, specifically one reminiscent of RPGs rather than historical reality. He finds himself reborn into the world of "Beast Fantasy 4," a popular RPG series he played extensively in his previous life. To his dismay, he is reborn as a citizen of the villainous Behemoth Empire, destined to be an enemy of the eventual hero.
Determined to avoid the empire's prophesied downfall and his own likely demise as a defeated antagonist, the protagonist, now named Jira, resolves to live a quiet, unremarkable life as a commoner. He is ten years old and lives with his parents and younger sister, Seren. His peaceful existence is disrupted when Seren, an adventurous eight-year-old, wanders off. While searching for her, Jira witnesses a confrontation between two children: Saraka, accompanied by several adults, and a lone girl. The girl, revealed to be from the Robos tribe, is being bullied by Saraka, who belongs to the Hanuma tribe.
Seren impulsively intervenes, declaring bullying is wrong. This enrages Saraka, who orders his adult escorts to attack both Seren and the Robos girl. Jira, despite his desire to avoid trouble, is forced to act to protect his sister. He reveals he can use magic, a skill learned from his past life's knowledge of "Beast Fantasy." He quickly incapacitates Saraka's adult entourage with basic fire magic. Saraka, shocked by Jira's power, retreats, but not before Jira learns the Robos girl's name is Forte.
Forte, revealed to be the daughter of the Robos tribe leader, explains that her tribe and Saraka's Hanuma tribe are both subjugated by the Behemoth Empire, and they are present in the capital as hostages. She also makes a cryptic remark about striking the empire with a "blue fang," which Jira recognizes as a line spoken by Ulforte, the fourth of the "Twelve Apostles of the Imperial Guard," powerful antagonists in "Beast Fantasy 4." This confirms Jira's suspicion that he is not only in the game's world but is also destined to become one of these antagonists, specifically the twelfth-ranked Jira-t.
Realizing his passive avoidance strategy is insufficient, Jira decides he must become stronger. He declares his intention to join the army, but secretly plans to use his remaining five years before mandatory military service to train. He travels to the secluded "Sage's Hermitage," the training ground of the protagonist of "Beast Fantasy 4," Cero. There, he meets the Sage, who is revealed to be a talking tanuki, "Sage Pom Poko." Jira is initially rejected due to his "beastly" smell but is accepted after washing himself thoroughly.
Jira undergoes three years of rigorous training under Sage Pom Poko, learning to control his emotions, accumulating vast knowledge, and eventually sparring with the Sage himself. He masters advanced fire magic and begins to learn "Chisei-jutsu," a unique power system in the "Beast Fantasy" series. After three years, he has surpassed the Sage's initial teachings and has two years remaining before his mandatory military service. He decides to stay longer to learn the series' ultimate finishing move.
During his training, a young boy stumbles upon the hermitage, weak and disoriented. Jira realizes this boy is Cero, the protagonist of "Beast Fantasy 4." Cero reveals his village was destroyed by the Behemoth Empire, and his parents were killed. The Sage, though powerful, refuses to directly intervene, citing his duty to the God of Wisdom. Jira, witnessing Cero's despair and realizing he knew this would happen from his past life as a gamer, is overcome with guilt for his inaction. He apologizes profusely to Cero, understanding that his past-life perspective was too detached from the reality of this world.
