The narrative picks up with the protagonist, Chris (a former man now in a woman's body due to a magical potion found in an ancient ruin), bound and transported in a dilapidated carriage. Chris, an 18-year-old adventurer, recounts the events leading to her current predicament. While exploring an uncharted ancient ruin, she triggered a trap and was poisoned. In a desperate attempt to survive, she consumed five vials of mysterious ancient potions. The poison was neutralized, but the potions transformed her into a young girl, causing her to lose all her acquired treasures and equipment. After escaping the ruin, she was unfortunately picked up by slave traders, who now view her and the other captured women as valuable merchandise.
The slave traders stop for a meal, and Chris, still bound, demands her ropes be untied. The other female slaves, resigned to their fate, are too afraid to help, but a kind girl named Isla offers Chris her bread. Chris, inspired by Isla's kindness but frustrated by their helplessness, rallies the other women, urging them not to give up hope and to fight for their freedom. She asserts that giving up is akin to death and that they must fight for a chance at escape. Isla, witnessing Chris's defiance, calls her "Onee-sama" (older sister), a term that deeply unsettles Chris, who is still grappling with her new female identity.
Their journey is violently interrupted when something strikes the carriage, creating a hole in the roof and causing it to tilt. This chaotic event presents an opportunity for escape. Chris urges Isla to untie her, and they, along with four other young women, flee the carriage amidst the confusion. They witness the slave traders being overwhelmed and slaughtered by goblins. Chris, realizing the immediate danger, makes the brutal decision to kill a paralyzed woman who is unable to escape, preventing her from suffering a worse fate at the hands of the goblins.
They escape into the wilderness, and Chris, despite her physical limitations and lack of proper footwear, leads the group. They fashion a raft and travel downriver, a journey that reveals Chris's body possesses unusual resilience and stamina, as she experiences no fatigue or injury after building the raft and running barefoot. During their journey, they encounter a military patrol led by a charismatic young nobleman named Leon. To gain entry into the fortified city of Terraveran, they feign injury and are taken in by Leon, who suspects their true identity as escaped slaves.
Upon arriving at Leon's opulent mansion, Chris, Isla, and another girl named Palmyra are bathed and dressed in fine clothes. Chris is shocked by her own stunning transformation into a beautiful young girl, a reality that finally sinks in. Leon reveals he knew they were escaped slaves from the beginning, as his unit was hunting the slave traders. He proposes a dangerous mission: to infiltrate the city's lord, Guibunag, who is revealed to be the mastermind behind the slave trade. Chris reluctantly agrees, despite her deep aversion to becoming a slave again, after Leon offers a substantial reward and the promise of a chance to return to her original body.
The mission involves Chris, Isla, and Palmyra posing as slaves to gather evidence against Guibunag. They are assigned to a special unit, including Leon, his gruff subordinate Leopard, a stoic intelligence officer named Regnum, a seemingly frivolous captain named Rupert, a grim-looking priest-like figure named Regnum, and a young woman named Irene, who is revealed to be an enchantment mage capable of communication and tracking. The plan is for Chris and the others to be handed over to Guibunag, identify other slaves, and await a signal for a raid. The narrative ends with the group preparing for their infiltration, with Chris still struggling with her new identity and the moral implications of her past actions.