A mysterious Ludens woman who was brought to the mysterious space known as the 'Strain Area' and awakened to self-awareness through someone's intervention. She now lives with Shina Ninomiya, who is also her namesake. (She has large breasts and thick, healthy thighs. She has an otaku streak and cares for her friends, but feels like a junior/underclassman. Because of her large chest, her friends sometimes get annoyed with her internally. She ends her sentences with '-ssu,' making her sound like a typical junior. Despite being so glamorous, why is she wearing hot pants?! You can tell her chest is huge even through her clothes! Her hair is red, ankle-length, and tied in a ponytail. Also, she dies quite often. It's practically a running gag! Blue eyes.) The third daughter of the Hiwatari family.

Every action she takes is driven by 'murderous intent.' However, since Sayaka manages her bank account, she can't act too tough. The eldest daughter of the Hiwatari family. She speaks with the refined tone of a high-class lady. A Ludens.

The only sane one among the three sisters... maybe. She is a musician who composes and is incredibly famous as an artist. However, since Sayaka manages her bank account, she can't act too tough. The second daughter of the Hiwatari family. Her speech is relatively normal. A Ludens.

Female. She has short brown hair and sometimes wears glasses. She has a unique sense of style, evaluating revealing outfits as 'not bad.' She can be a bit airheaded and a crybaby, but she is kind-hearted and loved by everyone (in fact, Mai Toyama, the protagonist of the sequel, sarcastically remarked that she 'looks like she couldn't even kill a bug'). She loves games and has a bit of an otaku streak with strong preferences. She wears a checkered skirt and tights. She is the one who named Sayaka, making her something of a mother figure to the three sisters. She is just a tiny bit obsessive and a tiny bit yandere toward Sayaka. She has a C-cup chest and isn't particularly thick or voluptuous. She is a Ludens. She acts as the caretaker for the Hiwatari sisters.