Inui, Shinju

Shinju is described as a relatively tall girl for her age. Like her sister, she possesses pale pink hair that falls at the length of her upper back. But instead of possessing sharp hazel-colored eyes like the latter, Shinju's eyes are more droopy and light brown in color.

Given her towering stature and ample bosom, her appearance would leave those to assume that she's an adult, when in reality, she's only a middle schooler.

Unlike her sister, who is rather blunt and headstrong, Shinju is a timid yet kind-hearted girl. She is shown to get nervous easily, especially when meeting new people, as seen during her first meeting with Gojo and Marin. This aside, Shinju strongly admires and loves her sister, working as her cosplay photographer while also creating an online account to share her sister's work. Shinju likes the Flower Princess Blaze alongside Sajuna and Marin. Her favorite character from the series is the older brother Soma, due to his caring nature, as he reminds Shinju of her sister.

Shinju is aware of her mature figure, particularly her chest, and is shown to get embarrassed about it. She also calls herself "fat" in the Japanese dub of the anime.

Like her friends and "big" sister, she is also interested in trying out cosplay but, contrary to the others, she wishes to cosplay as a boy. Her big chest, however, has proven to be a hurdle in achieving this.

(Source: Sono Bisque Doll Wiki)