Rei is a calm and mature girl. Due to her mature attitude, she has a tendency to keep a certain amount of distance from others (for example, not giving her opinions, or hiding her troubles from others, as shown in the event outside/inside where she overworked herself in order to perfectly play the hard bass parts she was given during her and Masuki's gig). However, later in the story, and mainly thanks to her bandmates' effort, she starts to open up more easily. She is also sometimes mistaken for an adult due to her mature appearance; in an area conversation, she says the movie theater workers couldn't believe she's a high school student.