The story begins with Sumiragi Jo and his friend Takeda Shion leaving an arcade after exams. It's a cold winter day, and Jo, who dislikes the cold, complains about his mother's insistence on studying for college entrance exams. As they wait for their train at a large station, Jo is suddenly bumped from behind by someone rushing up the stairs. This causes Jo to lose his footing and fall down the stairs, with Shion falling after him. Jo hits his head hard and loses consciousness.
He awakens to find himself in a strange, unfamiliar place, being tended to by a beautiful woman with blonde hair named Rasen. To his shock, Jo discovers he has transformed into a girl, complete with a female body and wearing a rough, off-white tunic. He also finds a heavy metal shackle on his left ankle, chained to the floor. Looking around, Jo realizes he is in a stone chamber, not a train station, and the area is stained with blood. Several figures in black robes lie dead or incapacitated, while others in leather armor stand guard. Rasen explains that they are a mercenary unit who arrived to stop a dangerous ritual and found Jo in the process. They were attacked by the "followers of the Black God," and Jo was about to become a sacrifice.
Jo is taken to the mercenary unit's lodgings. He learns that this world is different from his own, with fantasy elements like magic and mercenaries. He is given a blanket and later, a room. The next morning, Jo is introduced to Marika, who handles administrative tasks, and Takuto, a younger mercenary. They help him get dressed in more appropriate clothing and prepare breakfast. Jo struggles with the local language and customs, including a prayer before meals. He also learns that his own clothes and scarf were recovered.
Jo is brought before the mercenary captain, Tachibana Kyle, and Rasen. Kyle confirms that Jo is an "outsider" from another world, brought here by the followers of the "Black God." He also astutely deduces that Jo was originally male. Kyle explains that such occurrences are rare but have happened before, with individuals' bodies transforming upon arrival. Jo believes he died in his world after falling down the stairs, making a return unlikely. Kyle agrees to take Jo under the unit's protection, on the condition that he keeps his original gender a secret. He suggests Jo learn the local language and help Marika with her work.
Jo then remembers Shion, his friend who fell with him. Kyle agrees to investigate Shion's whereabouts, sending a messenger bird to the local lord. The story ends with Jo contemplating his new reality, the possibility of never returning home, and the challenges he faces in this new world, all while trying to adapt to his female body and the unfamiliar customs. He also learns that the current season is a time of increased activity for the "Black God's" followers, making the situation more precarious.
