Being Harumi's sister, she bears resemblance to Harumi. Like Harumi, she's really tall and has a big chest. She has dark purple hair styled in a bowl cut reaching the height of her chin, with a longer bang on the right side of her face just long enough to touch her shoulder. Back in her Aihara Academy days, she had longer hair, which she kept in a ponytail.
Mitsuko is a cold and serious person, similar to Mei. However, unlike Mei who can be concessive, she firmly believes that the school's rules should be kept at all costs. According to Harumi, during her time as the student council president, she ruled the school with an iron hand. However, she is capable of being kind to certain individuals.
- "Mitsuko" can have different meanings depending on the writing, such as 光子 ("shining child"?) or 睦子 ("harmonious child"?). Mitsuko's name, however, has no actual meaning as it's written in Hiragana, although "子" is the kanji for "child". "Taniguchi" (谷口?) means "mouth of a valley".
- Based on Harumi's description, Yuzu imagined Mitsuko as a Harumi look-a-like dressed like a stereotypical Japanese delinquent and holding a club with nails running through it.