Usami Renko (First daughter) A genius since her childhood, she was accepted into Kyoto University. Her mind is sharp, but her often sloppy behaviour means serious people often have an unfavorable view of her. Being from the remote countryside having suddenly left as a genius made her relatively famous in her hometown. On the other hand, she is often thought of as a weirdo, which isn't helped by the rumors of her participating in an occult cirle in university.

Usami Imouto (Second daughter) The highschooler younger sister who grew up in Renko's shadow. She's a model student with excellent grades, yet her abilities still do not even compare to her older sister's academic prowess. Seeing her sister get excpetional grades despite never even having an air of studying, or hearing stories of her joinig a weird circle in her university makes her feel envy and a mess of other emotions, yet her admiration towards her has never wavered. She loves her sister.

At first I thought about naming her Usami Sakurako, to name her after a flower like Renko and Sumireko are, but I felt like giving her a name would make her too much of an original character so I didn't. Renko = 蓮子 -> 蓮 = lotus, Sumireko = 菫子 -> 菫 = violet, Sakurako = 桜子 -> 桜 = cherry blossom

Lookalikes of Kosuzu and Akyuu. The younger sister's classmates. They probably have names like Suzuko and Aki. Aki is from a distinguished family but wanted to try having a part-time job so she works at Suzuko's family's used book store from time to time.

A primary schooler hiding infinite potential. A last child full of energy. Her favourite T-shirt is one she got from Renko wit "BIG TITS" written on it. Maybe thanks to that, she will grow up to have a glamorous body, but that is still far in the future.

Just like for the second sister, I did think of a name for her too, she would be something like Usami Asako. I'm not sure about that name. It might be a typo by the author or I might have misidentified the kanji (though it pretty clearly seems to be 麻 despite the low resolution). Also since I couldn't find this as a name, I'm not sure if the reading's correct. Asako = 麻子 -> 麻 = cannabis / hemp