Yūsaki Riko

Riko Yuusaki is  Rito Yuuki '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 Lala had created another invention called Koro-Koro Danjo-Kun/Change Boy Girl-Kun to change Rito back into Riko anytime.

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. She has a great bust size which even makes Nana jealous. Haruna and Mikado apparently finds her cute and Momo even mentioned that Riko is still her type even in this form.

In To Love-Ru Darkness, her hair is now all straight and for some reason the back of her hair is noticeably shorter than it was when she appeared in To Love Ru. Her 3 sizes are 85-55.5-84

Personality
Rito still retains his usual personality   and   behavier   but tends to feel uneasy  when in this form due to the exaggerated body change, regardless of how many times he turns into Riko. However he tries to pull off a girly personality when around characters who don't know about his/her condition, even if they do know of Riko's true identity, Rito is prone to act in a slightly more female manner in this state. By turning into Riko has a slight understanding of what  Run  and  Ren  go through when changing.

Comically, Rito does seem to consciously struggle with the gender he is placed in, such as when teased about it by Mikan (who can't seem help but tease "Her" by reffering to her as her older sister - this does seem to hint, as Momo noted, that Mikan might be something of an "S" around Rito). Riko appears to be quick enough to adapt to keep up a good act and function in a role, such as dating Saruyama or working in Mikado's clinic.

Rito's legendary falling issue is also present in this form, but it can also result in "her" being gropped instead of doing so to others.

Plot
The character is initially created when Lala's device, designed to make a female's body, chest and figure perfect, blows up when Yami attacks Rito and sends him flying into it. After emerging from this cloud, Rito had been transformed into a female form. At home, Mikan and Lala both teased "her" on the matter, eventually causing her to run away. After being attacked by the Principle, she was taken in by Saki Tenjouin, until Lala arrives in an untimely manner and returns her to her male form right infront of Saki - both of them naked in a bath. 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 sort amount of times at rare occasions. While as Riko, it is often stated that she is Rito and Mikan's cousin to avoid suspicion.

Every now an then someone (either Lala or Momo) would force to change into Rito merely for humor or for illustrations. Some times she would appear in Saruyamas love fantasies for such things like Valentines day.

Later i n  To Love Ru, Riko reappeared when Lala tried to get Rito to go on another date with Saruyama, but, due to being chased by Yami, Rito was transformed while running away. She later ran into Yuu Kotegawa who protected her from the Principal, where she transformed back into Rito right infront of him.

In To Love Ru Darkness, Lala transformed Rito into Riko to show Mea  Kurosaki   an illustration on Run/Ren's nature. This marks the second time most of the characters present have seen the form, with Nana coming to envy how Riko's chest is so large and Sairenji coming to consider the form cute. This change forced Rito to leave the school early and return home (especialy when Saruyama came in), with Mea and Lala continuing to harass her along the way and even dressing her up in a maids outfit. When "she" is finally alone, Rito takes a moment to scrutanise his female form, only to be caught by Momo, who takes it as evidence of his fasination with the female body. This meeting eventually leads to Mea returning, as planned, and discovering Momo's true personality. the two girls then reach an agreement to become friends, and even co-operate on the Harem plan, but Mea notes she cannot help recruiting Yami into it. the two then started to "play" with Riko, only to be caught by Mikan right when he turned back

Riko makes a second re-appearance in darkness, where Momo transforms Rito and dresses her as a nurse to help in Mikado's clinic (who took a liking to her). She accompanied Yami to the basement of said clinic to see what had happened to Tearju, and helped convince Yami to try getting closer to her creator. When it is revealed that Tearju had accidentally activated a dangerous automaton in he basement, Riko and Yami tried dodging it's attempts to "apply first aid" but ran into each other, in a comical reverse of their usual playaround, Yami ended up groping Riko's chest. After destroying the auctomaton, Yami found that Rito (completely naked) had turned back to normal and was unconscious. She later called it unfair of him to turn back in that situation, as she caught sight of "the beast" and was forced to dress him, which gave her an intense blush.

Trivia

 * Due to being the female form of Rito and him being Mikan's brother, Riko would technically be Mikan's sister (A fact Mikan exploits for her own amusement by calling her "Onee-san").
 * Ironically, Rito's clumsiness carries over to this form, which resulted in her breasts being gropped by Yami. When Riko imitated Yui, Yami asked in bewilderment if "she" should be the one saying so.
 * The same thing roughly happened with Nana as well, where the young princess ended up slapping Riko, due to feeling like she was insinuating that her chest was small.