Kanji Saeki, a 32-year-old single farmer living a solitary life in a remote Japanese mountain village, is unexpectedly visited by Christina Brunhilde von Melvis, an 18-year-old blonde woman in full Western-style armor, carrying a longsword. Christina claims to be a knight from the Euryde Kingdom, a "defeated soldier" fleeing a barbarian invasion after the fall of Mozangate Fort. Kanji, initially dismissing her as a cosplayer, is nonetheless kind and offers her shelter when she proves too exhausted to walk. He helps her bathe and provides a yukata, during which she falls asleep in the tub. Kanji carries her to bed, inadvertently seeing her naked, an event that will later become a significant point of cultural misunderstanding.
Confused by Christina's unwavering "setting," Kanji contacts his former girlfriend, Honami Izawa, a pragmatic Foreign Ministry official with a hidden passion for subculture. Honami, intrigued by the "female knight," suggests Christina might be from another world. This theory gains traction as Christina reveals her complete ignorance of modern Japanese concepts like buses, rice, and toilets, while also demonstrating real magic, including a language-translating helmet and basic fire magic. She explains her escape involved an unconscious use of a forbidden transfer magic scroll and speaks of goblins and orcs. Christina expresses deep guilt over her kingdom's fall and anxiety about her inability to return, a sentiment Kanji, despite his initial skepticism, finds himself empathizing with.
Honami arrives, quickly switching from excited fan to professional investigator. She confirms Christina's claims of magic and her helmet's translation ability. Christina, flustered by Honami's probing questions, particularly about Kanji seeing her naked, becomes even more confused when Honami playfully suggests marriage to Kanji as a possible future. The revelation of Kanji's past relationship with Honami further complicates Christina's emotional state, as her world's strict customs clash with Japan's more relaxed norms.
The Japanese government, alerted to the potential for unknown pathogens, orders both Christina and Kanji into a Self-Defense Force hospital for a week of examinations. Kanji's farm is left unattended, and a typhoon strikes, devastating his crops. During their confinement, Christina shares her world's "fairy tales," which surprisingly parallel real-world disease concepts, highlighting the cultural differences and similarities. Kanji, reflecting on the seriousness of the situation, reassures a despondent Christina, sharing his own struggles as a farmer and affirming her knightly pride.
After three weeks (extended due to a false alarm with Kanji's middleman, Yao, and rigorous testing), both are cleared. Christina is confirmed to be Homo sapiens, suggesting a parallel world. Honami, compensating Kanji for his losses, orchestrates Christina's return. Christina, now elegantly dressed in modern clothes, confronts Kanji. Playfully yet earnestly, she demands he "buy her back" and "take responsibility" for seeing her naked and for his past actions, a culturally significant gesture of commitment. Kanji, flustered but touched, playfully teases her back, accepting her unspoken plea to stay. The story concludes with Christina, now "Chris," embracing her new life and a budding, if culturally complicated, relationship with Kanji, marking the end of his solitary life.
