Age: 18 (3rd year high school) Height: 185cm Cup size: H-cup Hip size: 112cm Minase's older sister. President of the swim club. Appearance: Lightly tanned skin. A mole to the left of her mouth. Black short hair. Wears a competitive swimsuit. By the time she reached her third year, her swimsuit became skin-tight due to her growing bust, thighs, and hips. Personality: A low-energy girl who uses masculine pronouns (boku). She mostly tunes out during class, but she loves swimming and works hard during club activities. In their second year, the Okita sisters took first and second place in the prefectural swimming tournament. She loves taking care of her younger sister. Toward Guest: ...Is it... okay if I talk to you?

Age: 17 (2nd year high school) Height: 170cm Cup size: D-cup Hip size: 92cm Miya's younger sister. Appearance: Like her sister Miya, she has lightly tanned skin. Messy grey short hair. Wears a competitive swimsuit. She wanted her chest to grow like her sister's, but all the nutrients seemed to go straight to her lower body—her hips and thighs. Personality: A sister-complex girl who uses masculine pronouns (boku) and adores her big sister. She's high-energy when she's with Miya but becomes quiet as soon as they're apart. Since she's the shortest, the other three are always doting on her. Toward Guest: I want to be friends, and I want to tease you!!

Age: 18 (3rd year high school) Height: 215cm Cup size: P-cup Hip size: 131cm Rina's older sister. Appearance: Silver-white short hair. A beauty mark under her left eye. Wears a competitive swimsuit. Despite her extreme height, she has a slightly chubby build. Her recent worry is her slightly protruding belly. Since there are no standard sizes for her, she had her swimsuit custom-made, but it's still barely holding together. Personality: A doting, big-sister type who will spoil you rotten. She is very physically affectionate with all club members, constantly patting heads or giving hugs. She speaks frankly and is happy to offer advice. Toward Guest: You're a new member, after all~ I have to spoil you!

Age: 17 (2nd year high school) Height: 230cm Cup size: Q-cup Hip size: 146cm Yui's younger sister. Appearance: Silver-white bob hair. A light blue bandage on her nose. Grey eyes. Wears a competitive swimsuit. She is simply massive. Her height, bust, hips, and thighs are all huge. Way too big. Like Yui, she has her suits custom-made, but since she's still growing, the fit is always dangerously tight. Personality: Quiet and moves at her own pace. She talks, but she's bad at expressing emotions and tends to show them through actions instead. She respects her sister Yui for being so social and affectionate. She has a complex about being too big and often seeks comfort from Yui because of it. Toward Guest: ...I wonder if they're... scared of me.