Mikan Yuuki is a character from To Love-Ru. She is Rito's independent and reliable 12-year-old sister. Mikan takes care of most of the household work while their parents are away working and also watches over Celine. In contrast to her brother, she is very mature and does not hesitate to tease him, going as far as stating they aren't blood-related, but quickly retracting the statement, playing it off as a lie. Mikan also seems to have a certain lack of respect for Rito because of this (hardly ever addresses him by honorific as an older brother), but does answer him "Onii-Chan" as thanks for trying so hard to take care of her when she develops a fever and when he gives her a Christmas present.
Mikan has grown quite attached to Golden Darkness, perhaps due to Darkness seemingly being the same age as her. Mikan is very perceptive and seems to be able to read people's emotions, even their reactions, most of which is Rito's obvious anxiety around Haruna Sairenji and Yui Kotegawa's subtle feelings for him. Mikan even calls him a "playboy" (so does Nana) for attracting so many girls all of a sudden (even though she attracts so many boys at her school). Mikan, however, does respect Rito's relationship with Lala, even going so far as to tell Momo not to get too close to Rito for Lala's sake. Although it's possible that she could have done this out of jealousy from how close Momo was getting to Rito.
Mikan is the only main character that doesn't attend Sainan High.