The story begins by introducing **Nohara Shingo**, a high school student who reluctantly acts as the "fake boyfriend" for **Nagamine Yuuki**, the school's most beautiful and popular girl. Shingo's role is to deter the constant stream of male confessors. However, Yuuki's elegant public persona quickly shatters in private, revealing her true self: crude, mischievous, and fond of teasing Shingo, whom she calls "Megane-kun." Shingo soon realizes that Nagamine Yuuki is actually **Yuuki-kun**, his childhood bully, who underwent a gender change due to a mysterious "disease" and transferred schools. Yuuki-kun forces Shingo to maintain the fake boyfriend charade, threatening him if he reveals her secret, and declares her intention to "ruin his life" as punishment for not recognizing her.
Their unusual relationship deepens through various school events and private interactions. Yuuki accompanies Shingo home after buying a video game, where Shingo's younger sister, Mitsuki, is easily bribed to leave them alone. Yuuki, who hasn't played games since her "new father" forbade it, uses her physical presence to distract Shingo during a fighting game, revealing a playful, un-acted side. During the Sports Festival, Yuuki, despite her athletic prowess, is forced into a "borrowed item race." She pulls Shingo from the crowd, dragging him to the finish line, claiming the "borrowed item" is "Otaku," then tears up the slip, hinting at deeper, unexpressed feelings or a desire to protect Shingo from embarrassment.
On Valentine's Day, Yuuki distributes expensive chocolates to the entire class, but later gives Shingo a small, handmade, "ugly" chocolate privately, calling it "pity." Shingo is surprisingly touched, seeing it as a sign of her growth. However, she then forces him to buy her an expensive cake for White Day, revealing her newfound love for sweets. She takes him to a ramen shop, a new experience for her, and her genuine excitement and loud eating habits, coupled with her hair-tying gesture, fluster Shingo, who she then teases for being "kyun-ed."
A class seat change leads to a boys' janken tournament for the coveted seat next to Nagamine. Shingo accidentally wins but, knowing Yuuki's true, troublesome nature, nobly forfeits his win to allow a fair lottery. Ironically, he still ends up in a desirable back-corner seat, only for Yuuki to swap with another girl, Yamane Sarara, to sit right next to him. Yuuki teases Shingo, claiming Sarara "hated" him, and whispers "See you tomorrow, Shingo" in his ear, leaving him flustered.
When Shingo falls ill, Yuuki visits him, initially appearing angelic to his feverish mind. She teases him but brings him cut apples and medicine, even "feeding" him an apple slice while calling him "livestock." Shingo is flustered by her "Nagamine-san" persona and close proximity. He tries to describe what he likes about "Nagamine-san" (her physical attributes), which Yuuki mocks, then force-feeds him medicine, knocking him out. Shingo's sister later implies Yuuki caught his fever, but Yuuki is perfectly fine the next day.
For the school festival, Yuuki is cast as a fake princess in a serious play. She takes the role seriously, practicing diligently. During a late-night practice session, she asks Shingo to be her scene partner for a romantic confession. Her performance is incredibly convincing, making Shingo's heart pound and almost fall for her, realizing her acting prowess stems from her daily "Nagamine Yuuki" persona. She then dismisses the lines as "cringey" and rewrites them. After the play wins 2nd place and Yuuki wins the Miss Contest, she pulls Shingo to the rooftop, asking to practice the romantic lines again. Her emotional delivery makes Shingo feel like a genuine confession, leaving him deeply flustered and admitting to himself that he almost fell in love, but doesn't want Yuuki to dislike him.
On April Fool's Day, Shingo plans to prank Yuuki, but she pranks him first, claiming she has a girlfriend. Shingo retaliates by claiming he has a "true girlfriend" (a junior librarian named Miyama-san) and no longer needs a fake one. This causes Yuuki to genuinely cry, revealing a deep vulnerability. Shocked, Shingo immediately retracts his lie. Yuuki then punches him in the jaw, knocking him out. Shingo wakes up on Yuuki's lap, with no memory of the punch, and Yuuki covers it up by saying he "fell and hit his head," teasing him with a cold stare.
From the initial dislike and forced relationship, Shingo's feelings for Yuuki have become deeply complicated, marked by confusion, frustration, and a growing, albeit reluctant, attraction, while Yuuki's teasing hides moments of genuine care and vulnerability.
