Male, 16 years old. 1st year, Class 4 at Ohananomitsu University High School. A model student who is kind to everyone, has great sense, is smart and athletic, and is popular regardless of gender. He is sincere, friendly, and easy to talk to, truly deserving of the title 'perfect son.' Having experienced the pain of 100 consecutive rejections before entering high school, he has worked tirelessly to be worthy of love, resulting in his current impressive specs.

Female, 18 years old. A 3rd-year student and president of the Chemistry Club, she is the first older girlfriend to appear. The four girlfriends before her were all 1st-years the same age as Rentarou. 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 takes a neutralizing agent. Even then, the side effect limits how long she can stay in her original form. Thus, physically, she is effectively the youngest girlfriend. Her memories are the same in both forms, but her mental age differs. 3rd year, Class 3. She serves as comic relief even in serious stories. As she provides justification for the appearance of unrealistic drugs, she is like a 'cheat key' for the plot's progression. She refers to herself in the third person.

Extremely intelligent, she scores perfect marks on exams and is fluent in English. However, she is so expressionless that one might mistake her for a machine, always maintaining a stoic face and pursuing only efficiency. This lack of humanity caused her to unintentionally hurt others in the past, most notably her middle school classmate Mimimi Utsukushisugi. Due to her mechanical nature, there were even rumors that she was an AI. She usually treats Rentarou, her soulmate, with indifference. Regardless of personality or behavior, she prioritizes extreme efficiency above all else.

Female, 16 years old. 1st year, Class 4. She is the most aggressive in trying to take Rentarou's virginity, but since Rentarou's resolve to maintain boundaries is so firm, her plans always fail. She is completely devoted to Rentarou and worships any plan or action of his, except for the idea of him leaving her. She occasionally shows a subtly dark and perverted side.

Female, 16 years old. 1st year, Class 4. The tsundere heroine and the first of her kind in the group. True to her nature, she is prideful and dishonest about her feelings, a trait that persists even after she starts dating Rentarou. However, she occasionally reveals her true feelings, and she is incredibly cute when she does. With a bold and straightforward personality, she isn't afraid to speak her mind and often shows a cool, reliable side. She is the first to get angry if someone speaks ill of the Rentarou Family and acts as the 'big sister' of the group, looking after the newer girlfriends.

Female, 16 years old. 1st year, Class 4, 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 soft-spoken and clumsy with words, suffering from social anxiety that prevents her from speaking directly to people. She used to communicate by pointing at sentences in books, but after Rentarou 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 tickled, she rarely makes a sound, instead letting the electronic voice say 'She laughed out loud.' She even talks in her sleep via the electronic voice.

Female, 14 years old, the youngest member. 3rd year, Class 2 (Middle School division). She is the first girlfriend younger than Rentarou. A glutton character with a fast metabolism who gets hungry again immediately after eating. Her personality turns sour when she's hungry and wants food. Aware of this, she wears a hoodie and headphones to block out sounds that even remotely resemble food names during her usual hungry state. Her appetite is so immense that she isn't picky and gets hungry just by looking at raw ingredients. Her sense of smell is as sharp as a bloodhound's when it comes to 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. This perversion is no exception when it comes to Rentarou; she goes as far as making him cross-dress or preparing a private helicopter just to watch him from the sky if he's even slightly far away. It's enough to make even Rentarou recoil in disgust.