|Relatives||Chihiro Shindou (twin sister)|
Kei is very athletic and enjoys running. She is a star player on the school's girls varsity basketball team despite being only a freshman. Her personality is outgoing and energetic, the opposite of her quiet and reserved younger* twin sister Chihiro Shindou.
Kyosuke Tsutsumi became infatuated with Kei after he spotted her running down the street during Christmas and briefly filmed her with his video camera. Later, he tracks her down and gets her to agree to let him follow her around and film all her daily activities. Eventually he falls in love with her.
Mizuki Hayama idolizes Kei, a fellow basketball player, to the point where Mizuki sometimes has yuri fantasies about her.
Kei has strong unacknowledged feelings for her lifelong childhood friend, Hiro Hirono. In elementary school she had formed an inseparable trio with herself, Hiro, and her twin sister Chihiro Shindou (who at the time was very outgoing and energetic like Kei herself). The young Chihiro and Kei often competed for Hiro's attention in doing fun activities. One day when she was 12, Kei stole Hiro away and dragged him to the beach without telling Chihiro. Chihiro tried to run down the street after them, but she was struck from behind by a car and grievously injured. Kei bitterly blamed herself for causing the accident, and she now believes that she is unworthy of Hiro's love because of it. This is because she believes that Hiro would have ultimately ended up with Chihiro if not for the accident. Kei's guilt over the accident blocks her from confessing her true feelings to Hiro.
Kei masks her feelings by instead mothering Hiro, taking care of him, feeding him, and so on. This continues on into high school.
Eventually, with the help of Kyosuke Tsutsumi, she learns to let go of Hiro, and she and Kyosuke eventually become a couple. She later reconciles with Chihiro in Melodies episode 5, where the twin sisters finally reunite.
* Note: In Japan, the term 'younger twin sister' is not an oxymoron. Identical twins are distinguished between 'younger' and 'older' siblings, even if they are born only a minute apart.