Hotaru Mizushina (水科 蛍 Mizushina Hotaru) is one of the main characters of the series. She is a student in the second year of high school and the childhood/best friend of Yuma Okazaki whom she leads a romantic relationship with and the girlfriend of Fujiwara.
Hotaru is a short teenage girl with purple hair that has a ponytail on the left side with bangs hanging over her eyebrows, purple-yellowish eyes and Yuma Okazaki mentions that Hotaru has big breasts despite having a small body.
Hotaru has a secretive and non-revealing nature whose motives are seemingly constantly changing and end up being unpredictable. At first impression, she could be described as a tease, always cheering on the romance between her friends. She seems generally extroverted, although she considers herself to have no own friends beside Yuma Okazaki. When she was younger, she had a tendency to be the victim of bullying, due to being quietly and weak - which still occasionally occurs to be the case through her high school time, although the motives of her fellow students for it have migrated to jealous remarks.
There are dark sides to Hotaru that she keeps hidden from the outside world; She is emotionally manipulative, tricking Yuma into erotic actions with her under the guise of practice between female friends, trying to make her confused about her feelings towards her best friend in order to wake up possible romantic feelings. Hotaru wants to feel needed and does not shy away from mind games in order to have Yuma chase her. Afraid of her own feelings for her only friend, she participated in a series of dating random boys from her school, hoping it would inspire jealousy from Yuma's side, while holding no personal attachment to these men. This eventually led to an agreement with her current boyfriend, Fujiwara, who dislikes the idea of romance but he likes to have sex, making it the ideal relationship for Hotaru to cope with her primarily unrequited feelings. In order to keep this settlement up, she even endures domestic, physical violence and forced sexual interactions from Fujiwara, always excusing his wicked actions and not minding his side affairs with other women. Hotaru has no issues with physical contact, being able to have meaningless erotic interactions with others and showing off her body to elder men for her part-time job. She is dominant and intrusive during contact with Yuma, whereas her contact with men is submissive and apathetic.
- "Do you really want me to kiss you?" - Hotaru to Yuma Okazaki (Source Unknown)
- The name Hotaru means "firefly" (蛍).
- Hotaru's surname Mizushina meas "water" (水) (mizu) and "grade" (科) (shina).
- Hotaru likes to tease Yuma Okazaki and she is aware of her actions.
- Hotaru does not know if she really has feelings for Yuma and she sometimes shows certain expressions when she is with her. But, it is not clear whether she has romantic feelings for Yuma or not.
- Hotaru lives next door to Yuma.
- While Fujiwara is considered to be the most handsome boy at school, Hotaru is considered to be the most beautiful girl at school.