The protagonist awakens in an unfamiliar, spacious room, having seemingly fallen in the bathroom of her own home after a bath. She finds herself naked, wrapped only in a towel, on a comfortable bed. A man with striking golden-brown hair and grey eyes, whom she finds incredibly attractive and of a military type, enters the room. He immediately pulls off her towel, leaving her exposed. Despite her protests and attempts to hide under the covers, he restrains her and initiates sexual activity, which she ultimately accepts, finding it surprisingly pleasurable.
The next morning, she wakes up sore and disoriented, realizing she is in a world different from her own. The room's opulent furnishings and the man's non-Japanese appearance lead her to suspect she has been transported to another world, a theory seemingly confirmed when she discovers she can understand a book written in an unknown script. She learns the country is called Christal, and the territory is Jailo. The man, who reveals himself to be Grace Key Tailard, the captain of the Fifth Division, explains that she is a "Spirit Guest," summoned by spirits. He informs her that she cannot leave the room due to the dangerous surroundings, which are prone to monster attacks. He arranges for her meals to be brought to her room and provides her with a maid's uniform, promising to find her proper clothing and a place to stay once the female staff, who were evacuated due to monster activity, return in about a week.
Grace explains that magic exists in this world, demonstrating by conjuring fire. He also reveals that she possesses magic, albeit unusable for now, and that a spirit resides within her, acting as an interpreter and translator. He offers her three options for her stay: the current room, a nearby town, or the capital, but due to the dangers and her inability to ride a horse, staying in Grace's room is the only viable option. He expresses concern for her safety, warning her not to leave the room.
Later, a subordinate of Grace, a younger, more cheerful man with green eyes, arrives to discuss work. He accidentally discovers the protagonist in the room, leading to an awkward situation where he playfully propositions her, much to Grace's annoyance. Grace intervenes, physically separating them and emphasizing that the protagonist is a "Spirit Guest" and must be treated with respect. The subordinate, intrigued by the situation and Grace's unusually gentle treatment of the protagonist, jokes about their relationship.
Grace brings her books, including one about a hero, and they discuss the nature of spirits and the possibility of returning home, which seems unlikely. He also reveals that spirits summon guests to potentially improve the world. The protagonist learns that the staff will return soon, and she will be assigned a guardian and a place to work. She also discovers that the world has a history of heroes and that spirits are capricious beings who summon guests as a "play."
The next day, Grace brings her more books, including fantasy novels, and they discuss the world's customs. They also have a playful argument about who should sleep in the bed, with Grace insisting she take it. They eventually agree to share the bed, though with ample space between them. Grace reassures her that he will not initiate further intimacy, emphasizing her need to value herself. He also reveals that the spirits summoned her, and that the spirit within her is responsible for the automatic translation.
The following day, Grace's subordinate, a cheerful man named Riel, visits again. He accidentally discovers the protagonist, leading to another humorous exchange. Riel is surprised by Grace's protective behavior towards her, and they discuss the protagonist's status as a "Spirit Guest." Riel also mentions rumors about a woman being seen in Grace's room. The protagonist, still adjusting to this new world, continues to learn about its customs and magic, with Grace patiently answering her questions.
