Mariko is Nanako's classmate - she sits close to her - and is immediately attracted by her; she is a very beautiful girl who, not differently from the others, wants to become a member of the Sorority, and is very proud of her beauty. She wants Nanako to become her best and closest friend, and is very jealous of Nanako's friendship with Tomoko. For this reason, she'll try to undermine this relationship, telling some lies to Tomoko. She passionately defends Nanako in several occasions, but sometimes her behaviour is excessive; her sometime strange attitude towards the others is mainly caused by her serious family problems (the relationship between her parents is in a crisis and because of her father, Mariko completely distrusts men...). For some time, Mariko will risk losing forever Nanako's friendship. Mariko has very deep feelings for Kaoru, and in time she'll also become a friend of Tomoko's (only in the anime version).