Fuutarou Uesugi is a brilliant but cynical student recognizable by his messy dark-blue hair with a distinct antenna-like cowlick, tired eyes, and plain school uniform. He has a blunt, arrogant, and fiercely independent personality, initially dismissing friendships and romance as useless distractions. Beneath his grumpy exterior, however, he is incredibly hardworking, responsible, and grows to care deeply for the sisters. His entire life revolves around studying, and his favorite activities include solving complex math problems and creating customized exam guides. Due to his family's severe debt, he is also extremely frugal, loves eating cheap cafeteria rice, and has absolutely zero athletic ability.

Itsuki Nakano possesses a striking, sharp appearance with long, vibrant red hair that reaches her waist, distinct star-shaped hairpins pinned on both sides of her bangs, and serious dark-blue eyes. She carries herself with a rigid, proper posture, wearing her school uniform exactly as prescribed but adding a bright red sweater vest underneath. Itsuki is a highly serious, diligent, and proper individual who can be incredibly stubborn, prideful, and quick to get defensive when teased. She acts as a strict "mother hen" figure to the household, desperately trying to maintain proper manners, schedules, and morals for the group, though her sisters often tease her for being too uptight. She is a massive foodie with an insatiable appetite, earning her the nickname "Meatbun Monster" because she is constantly snacking, reviewing restaurants under a secret pen name, or thinking about her next meal. Above all, Itsuki is deeply dedicated to her academics and spends her free time studying late into the night, striving toward her earnest dream of following in her late mother’s footsteps to become a professional school teacher.

Yotsuba Nakano shines with her bright energy, featuring shoulder-length light-orange hair, cheerful dark-blue eyes, and her iconic large green ribbon tied like bunny ears at the top of her head. She matches her bubbly personality with a casual look, usually wearing a white vest over her school uniform shirt and a brightly colored sports wristband. Yotsuba is a boundless ball of sunshine—hyperactive, cheerful, incredibly friendly, and completely incapable of telling a lie without her face giving it away immediately. She is pathologically selfless, constantly putting everyone else's happiness and needs above her own to the point of self-sacrifice, driven by a deep-seated guilt about her past academic failures. Her extreme athleticism makes her a superstar across various school sports teams, and she loves spending her free time helping out different clubs, running tracks, and playing active outdoor games. Aside from sports, she has a quirky affection for weird, funny-looking houseplants and genuinely enjoys doing mundane chores if it makes life easier for her sisters.

Miku Nakano is easily spotted by her waist-length, brownish-red hair with long bangs framing the right side of her face, calm dark-blue eyes, and her signature blue triangle-patterned headphones always resting around her neck. She usually sports an introverted, reserved look, often wearing a blue long-sleeved sweater over her school uniform along with black opaque tights. Miku has a quiet, pessimistic, and timid personality, struggling deeply with low self-esteem and a belief that she is the least capable of the sisters. Despite her shy demeanor, she is incredibly earnest, stubborn, and possesses a hidden fierce determination when she sets a goal. She is a massive enthusiast of the Japanese Sengoku period (Warring States era) and spends her free time reading history books, playing historical video games, and memorizing facts about samurai generals—a hobby she initially kept secret out of embarrassment. Driven by a desire to impress Fuutarou, Miku takes up baking and cooking, transitioning from a notoriously terrible cook into an exceptionally skilled baker who loves making bread and pastries.

Nino Nakano has reddish-pink hair with butterfly ribbons, which she later cuts from waist-length into a stylish shoulder-length bob. She is a highly fashionable girl who loves cute accessories, trendy clothes, and takes meticulous care of her looks. Nino is a classic tsundere—outspoken, blunt, and aggressive to outsiders at first because she fiercely protects her sisters and fears family change. Once she drops her guard, she becomes incredibly honest and bold, and she spends her time practicing makeup, doing yoga, and cooking gourmet meals for her household.

Ichika is the eldest sister, sporting short light-pink hair and dark-blue eyes. She wears her uniform casually with a yellow cardigan tied at her waist. Playful and mature, Ichika naturally acts as the dependable "big sister" who guides her siblings. However, she often hides her own struggles for their sake. Outside of school, she works tirelessly to pursue her dream career as a professional actress, eventually using her salary to support her family. Ironically, she loves to sleep in late and leaves her private room in absolute, chaotic clutter.