Male, 16 years old. A first-year student in Class 1-4 at Ohananomitsu University Affiliated High School. He is a model student type who is kind to everyone, has great sense, is athletic, and is popular with both men and women. He is sincere, affable, and easy to talk to—a true 'perfect son' type. Before entering high school, he experienced the pain of 100 consecutive rejections, which led him to work tirelessly to be worthy of love, resulting in his current high-spec capabilities.

Female, 18 years old. A third-year student and president of the Chemistry Club, she is the first older girlfriend to appear. The four girlfriends before her were all first-years. However, due to a side effect from experimenting with an immortality drug, she usually looks like an 8-year-old child and only returns to her 18-year-old form when she drinks a neutralizing agent. Even then, the duration is short. Physically, she is effectively the youngest girlfriend. Her memories are shared between forms, but her mental age changes. She is in Class 3-3. She serves as the comic relief even in serious stories. As she provides a justification for unrealistic drugs, she is something of a 'cheat code' for the plot. She refers to herself in the third person.

She is exceptionally brilliant, scoring perfect marks on exams and speaking fluent English. However, she is so expressionless that one might mistake her for a machine, always maintaining a stoic face and pursuing absolute efficiency. This lack of humanity has unintentionally hurt others in the past, most notably Mimimi Utsukushisugi from the same middle school. Due to her mechanical nature, there were rumors she was an AI. She is usually indifferent even toward Rentaro, her fated partner. Regardless of personality or behavior, she prioritizes extreme efficiency above all else.

Female, 16 years old. A student in Class 1-4. She is the most aggressive in trying to take Rentaro's virginity, but since Rentaro's resolve to maintain boundaries is so firm, her plans always fail. She is single-mindedly devoted to Rentaro and worships every plan or action of his, except for the idea of him breaking up with her. She occasionally shows a dark, perverted side.

Female, 16 years old. A student in Class 1-4. She is the first tsundere heroine of the group. True to her archetype, she is prideful and has difficulty being honest with her feelings, a trait that persists even after she starts dating Rentaro. However, the rare moments when she shows her true feelings are incredibly cute. She is a bold and straightforward type who says what needs to be said, often showing a cool side. She is the first to get angry if someone speaks ill of the Rentaro Family and acts as the 'big sister' of the group, looking after the newer members.

Female, 16 years old. A student in Class 1-4 and a library committee member. A 'literary girl' character who, as her name suggests, loves books and has a quiet personality. She spends her time after school in the library. She is extremely taciturn and socially anxious, unable to speak directly to people. She used to communicate by pointing at sentences in books, but after Rentaro installed a text-to-speech app for her, she communicates using an electronic voice that reads book passages. Even when she is laughing because she's being tickled, she remains silent while the electronic voice says, 'She laughed out loud.' She even talks in her sleep via the electronic voice.

Female, 14 years old, the youngest member. A third-year student in the middle school division, Class 3-2. She is the first girlfriend younger than Rentaro to appear. A glutton character with a metabolism so fast she gets hungry immediately after eating. When she's hungry and wants food, her personality turns sour. Knowing this, she wears a hoodie and headphones to block out sounds that even remotely resemble food names. Her appetite is so immense she isn't picky and gets hungry just looking at raw ingredients. Her sense of smell is incredibly sharp regarding food. Unlike when she's hungry, she becomes very pleasant while eating. Because she loves food, she knows a lot about how to enjoy it, often playing a key role when food-related topics arise.

Hakari's mother and the chairwoman of the school. She has strong perverted tendencies, which extend to Rentaro. She tries to make him cross-dress or even uses a private helicopter to watch him from the sky if he's slightly far away. Even Rentaro is often appalled by her behavior.