The protagonist, a college student, has just cleared the "Ayano Route" of the dating sim "Melody of Love with My Sister," a notoriously difficult hidden route. He expresses satisfaction with the scenario but laments the presence of the villain, Reiji Shirosaki, whose escalating bullying in this route makes him a detested character. The protagonist falls asleep wishing he could meet Ayano, the game's heroine.
He awakens to find himself in the body of Reiji Shirosaki, the very villain he disliked, having seemingly been transported into the game's world. Initially disbelieving, he confirms his predicament through physical sensation and the reflection in his phone. He realizes he has completely possessed Reiji's consciousness and is now on a path to his character's ruinous end. With two days until the entrance ceremony, he resolves to alter the predetermined fate.
On the day of the entrance ceremony, Reiji's memories begin to surface, revealing a past of privileged education and subsequent social isolation and betrayal that warped his personality. Despite this, the protagonist finds it difficult to sympathize with Reiji's cruel actions towards the protagonist siblings. At the school, Reiji is met with fear and whispers from other students due to his reputation.
He encounters Ayano Shinomia, the heroine, and her brother, Yuto Shinomia, the game's protagonist. Ayano, initially appearing kind, gives Reiji a cold reception when he tries to wave. He realizes his villainous persona prevents any positive interaction.
In class, Reiji is placed with Ayano and two other heroines: Kotone Amashi, a popular but jealous girl, and Sayaka Kuromine, a seemingly perfect but manipulative "ojousama." Reiji expresses a desire to avoid them, as they become antagonistic towards Ayano in her route. During class elections, Reiji is assigned the role of librarian alongside Ayano. To avoid an argument with Ayano, who dislikes the assignment, Reiji offers to switch roles with Yuto, who reluctantly agrees.
The first week of school passes with Reiji attending classes diligently and participating in committee work, slowly beginning to shift the perception of him among some students, though many remain suspicious. He learns about an upcoming one-year student camp, a crucial event that determines which heroine route Yuto will pursue. Reiji resolves to avoid the campfire committee, a role that historically leads to trouble. He overhears students discussing Ayano's attractiveness, which he finds understandable as she is his first love.
Later, Reiji is asked by Sayaka to help with library duties due to a shortage of librarians. He agrees and finds Ayano working alone. They bond over their shared love for isekai fantasy manga, a conversation that significantly improves Ayano's impression of him. They exchange contact information. Reiji walks Ayano home, and she expresses gratitude for his help and kindness, noting his change in behavior.
The next day, during class, the camp groups are decided by lottery. Reiji is assigned to the campfire committee with Ayano. Yuto, however, intervenes, demanding to switch places with Reiji to keep Ayano away from him. Ayano tries to de-escalate the situation, but Yuto becomes increasingly aggressive, frightening her. Reiji intervenes, calming Yuto down and pointing out Ayano's fear. Yuto apologizes but warns Reiji to stay away from Ayano. Reiji reflects on Yuto's uncharacteristic behavior, suspecting it's a consequence of his own transmigration.
At the camp, Reiji and Narita, a mob character who assists Reiji, discuss the camp activities. Kotone approaches Reiji, asking him to switch to her cooking group, claiming she has a difficult person in her group. She specifically requests the campfire group, which Reiji finds suspicious as Ayano is in it.
During campfire preparations, Reiji and Ayano work together to transport firewood. Ayano expresses admiration for Reiji's stamina and asks for advice on training, leading to them exchanging contact information. They discuss manga, further strengthening their connection.
During dinner, Reiji eats extremely spicy curry, leading to a painful experience. Ayano offers him her mild curry, and they sit together, much to the envy of other students. They discuss the upcoming campfire activities, with Narita hinting at a planned "test of courage."
Kotone, meanwhile, is frustrated that Reiji didn't switch groups with her, as she had hoped to separate Ayano and Yuto. She returns to her cooking group, feeling resentful.
