Yūsaki Riko

Riko Yuusaki is Rito's female alter-ego, who is accidentally created through Rito being transformed into a girl by one of Lala's bizarre inventions which she dubbed Pai-Pai Rocket. Later, Saruyama,  Rito's best friend  falls in love with "Riko-chan" and asks Lala to invite her for a date; out of pity, she forcefully changes Rito into "Riko" so Saruyama can go on a date with Riko. After that Riko only appears for short amount of times at rare occasions. While as Riko, it is often stated that she is Rito's, and Mikan's cousin to avoid suspicion. By turning into Riko, Rito has a slight understanding of what Run and Ren go through when changing.

Appearance
Riko looks greatly similar to Rito as some characters have noticed, she has gold brown eyes and has slightly long straight hair and it's less spiky then Rito's. She is a beautiful girl (with a physical appearance resembling a tomboy) who gets much attention from men, such as Taizou Motemitsu, the  principal  and even  Kenichi Saruyama. Not only is  Riko quite attractive to a lot of boys, her looks are even appealing to girls like how she has a great bust size which even makes Nana jealous, Haruna apparently finds her cute and Momo even mentioned that Riko is still her type. Her breast were originally normal yet large size until due to the effects of Lala's invention they grew enormously large.

Trivia

 * Due to being the female form of Rito and him being Mikan's brother, Riko would technically be Mikan's sister.