Male, 16 years old. Class 1-4, Ohananomitsu University Affiliated High School. A model student type who is kind to everyone, has great sense, is good at both studies and sports, and is popular regardless of gender. He is sincere, sociable, and easy to get along with—a perfect 'mother's friend's son' type. Before entering high school, he experienced the pain of love and rejection 100 times, which led him to work hard to be worthy of love, resulting in his currently stable and high-spec capabilities.

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 Rentaro. However, due to a side effect from an immortality drug experiment, 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 duration is short. Physically, she is effectively the youngest girlfriend. Her memories are the same in both forms, but her mental age differs. Class 3-3. She serves as the comic relief even in serious stories and acts as a 'cheat code' for the plot by providing justification for unrealistic drugs. 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 and stoic that she could be mistaken for a machine, always pursuing maximum efficiency. This lack of humanity caused her to unintentionally hurt others in the past, most notably her former middle school classmate, Mimimi Utsukushisugi. Due to her mechanical nature, there were even rumors that she was an AI. She usually treats her destined partner, Rentaro, with indifference. Regardless of personality or behavior, she prioritizes extreme efficiency above all else.

Female, 16 years old. Class 1-4. She is the most proactive in trying to take Rentaro's virginity, but since Rentaro is firm about maintaining boundaries, 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 dumping her. She occasionally shows a gloomy and perverted side.

Female, 16 years old. Class 1-4. The quintessential tsundere heroine and the first one of the group. True to her nature, she is prideful and has difficulty being honest about her feelings, a trait that persists even after dating Rentaro. However, the rare moments when she reveals her true feelings are incredibly cute. She is a bold and clear-headed 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 junior girlfriends who join later.

Female, 16 years old. Class 1-4, Library Committee member. A literary girl character who, as her name suggests, loves books and has a quiet personality. She spends her after-school hours on library duty. She is extremely soft-spoken and socially anxious, making it impossible for her 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 finds something funny, she emits an electronic voice saying 'She laughed out loud' while laughing silently. She almost never speaks with her own voice, even talking in her sleep via the electronic voice.

Female, 14 years old, the youngest (Middle School 3rd year, Class 3-2). She is the first girlfriend younger than Rentaro to appear. A glutton character with a fast metabolism who gets hungry again immediately after eating. Her personality turns sour when she is 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, her personality becomes pleasant when she's eating. Because she loves food, she knows the best ways 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 Aijo Rentaro. 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 Rentaro feel repulsed.