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Atsuhiro "Akkun" Kagari is crazily in love with his girlfriend Non "Nontan" Katagiri. However, instead of showing his feelings, he hides them under a tsundere mask and prefers to store her photos and voice in his phone.

Akkun's best friend Masago Matsuo asks Nontan if she is really okay with a boyfriend who only spouts cruel words at her, but Nontan reveals that she knows Akkun doesn't mean what he says and believes he loves her. The next day, Akkun decides to walk home with her and gathers up his courage to hug her, although he ignores her out of embarrassment for three days after. A similar situation occurs after he kisses her, only he skips school for five days instead.

Akkun reveals to his younger sister Chiho Kagari on how he has perfectly calculated Nontan's eating habits, including her average number of chews per food item. While Chiho is absolutely disgusted with her older brother's stalker tendencies, she is likewise smitten with Nontan and doesn't hesitate in showing her hospitality, although she hides her own feelings as well.

Akkun recalls how he first started dating Nontan in middle school, where they gave each other their nicknames. After which, Nontan's mother gave him his first photo of her, and from there he started a habit of taking secret photos of Nontan and pasting them all over his room walls and ceiling. Nontan has no idea of his habit though.

Nontan visits Akkun's house after school on a rainy day. They watch a scary movie together with Chiho and Masago, who is always there playing dating sims because his console at home is currently broken. When Akkun goes to the kitchen to get Masago some coffee, he is followed by Nontan, and realises that she knows the location of items in his house, much to his delight as it makes them somewhat like a married couple.

Akkun goes over to Nontan's place for dinner, meeting her parents Seichiro and Tsugumi for the first time. The couple has a striking resemblance to Akkun and Nontan's dynamics in their relationship. When Akkun's parents Keita and Sakurako arrive to pick their son up, Nontan realises how Sakurako is similar to her mother but Keita is the opposite of her father with his clueless and boyish attitude.

Homeroom teacher Takumi Kubomura is having a hard time dealing with Konagi Irie, a cheerful female student that is utterly smitten with him. Both are utterly clueless: Takumi with Konagi's feelings for him and Konagi with Takumi's job as a teacher that she believes is him trying to spend time together with her. When he overhears Akkun saying mean things to Nontan despite them being dating, he questions Akkun about his feelings for his girlfriend, which are that of a pure-hearted young love. Wishing to understand and educate his students, he requests that Akkun say mean things to him in hopes of putting himself into Nontan's shoes.

Akkun advises Nontan to remember information by reading her notes out loud, where during this time he records her voice and uses her recitations to study himself. After the test, Nontan invites Akkun out on a date to the beach for the summer holidays.

Chiho is annoyed at how Masago has pretty much made the Kagari family residence his home by constantly playing dating sims there. Both of them grow close as she starts showing her own tsundere side to him as well.