One of Nao's best friends, and very loyal. She is boy-crazy and is very knowledgeable when it comes to that. She also keeps a book of all the hot boys she knows. Although Marina is very knowledgeable about them, she says she would never go out with anyone she doesn't like.
Later in the story, she starts going out with Mi-chan. Usually, once starting to date a boy, she breaks up with him shortly after. Her only serious boyfriend has been and is still Mi-chan. However, when she gets into a fight with him about her hair, she visits him with Nao's advice and sees him with another girl. However, the girl with Mi-chan was someone in his study group. Marina confesses that she knew Mi-chan was not cheating on her but feels insecure about their relationship because she worries that he will establish a new life at his new high school and that he will no longer have room for her and says she may break up with him. He waits for her to tell her that he does not want them to break up and she tells him she was only joking. He sighs with relief and Marina kisses his cheek, ending their fight.
