Yūki Mikan

Mikan Yuuki is Rito's independent and reliable 12 year-old sister. Mikan takes care of the housework while their parents are away on business and watches after 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 (she hardly ever addresses him by his 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 may not show it, but she cares very deeply for Rito and misses his company, to the point one could suspect her of having a brother complex, this more evident in the second OVA where she wondered if he would marry her if they were not blood related, and in the manga where she blushes every time another character mentions her brother, also in the 5th ova where after being hit by the pollen she tries to molest him while affectionately calling, "Onii-chan". Her brother complex may be the reason she rarely calls Rito "Onii-chan", less a lack of respect and more a sign of her wish that their relationship was something other than that of a brother and sister. She also states how she and Rito used to play together before Lala entered their lives.

It is later revealed that Mikan is terrified of thunder and lightning, though Rito would always comfort her. 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. 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 is fairly obvious that she could have done this out of jealousy from how close Momo was getting to Rito.

Personality
As a younger sister, Mikan is widely known for her maturity and reliability for her age. Her maturity is also quite unique, as while she is Rito's younger sister and the youngest character in the cast, she is arguably more adult than most of the other characters, and basically acts as a big sister, wife, or mother to Rito and all who live in her house.

Because she is very good at cooking and housework, she essentially takes care of her big brother. Rather than looking up to him, she instead treats him like he is her little brother, and rarely calls him "Onii-chan", as she used to. Mikan generally treats Lala the same way, enjoying her company like a little sister and pleased to see her brother's life becoming more entertaining upon her arrival.

Mikan is very perceptive, as she is good at understanding other people and noticing their feelings. She knew very quickly her brother's crush on Haruna, and Haruna's similar feelings for Rito as well. And she knows that Rito is too scared and immature to enjoy perverted things, and that Lala is innocent and quite childish, so she doesn't mind catching Lala naked in her brother's bed in the morning, and even treats it like something normal. But she particularly doesn't like Momo sneaking into his room at night and sleeping with him.

Like a big sister or mother, she would try to protect Rito from sexual temptations, and doesn't like it when girls with more perverted tendencies like Momo and Mea would do perverted things to him. She tries as often as she can to watch out whenever Momo gets the opportunity to be alone with Rito, and even guards his room at night to stop her from sneaking in and sleeping next to him. She also doesn't particularly like Mea when first meeting her, and though she tried to get to know Mea better after learning that she is Yami's sister, she finds that she cannot deal with her type and likely can't become friends with her.

Mikan seems to get along quite well with characters who are more level-headed, composed, and mature, such as Golden Darkness (Yami) and Rin Kujou. In To LOVE-Ru Darkness, despite being older than even Mikan's big brother, Rin seems to have become friends with her, and is astonished that someone like Mikan is the younger sister of someone like Rito. And Mikan is the only person whom Yami truly considers to be her friend. Rito explains that because she is so mature and reliable for her age, deep down, Mikan can get lonely without people she can relate with, and so she can use older friends who are like big sister figures to her, whom she can lean on (To LOVE-Ru Darkness chapter 5).

Rito Yuuki
As children, Rito and Mikan were very close, and Mikan still called him "Onii-chan". Because their parents were not often at home, Rito looked after Mikan and they spent their time together all the time, walking and playing outside together. Unlike Rito, who has grown up to become very clumsy, awkward and anxious, especially around women, Mikan has become hard-working, confident, and good with housework, far surpassing her older brother's maturity and reliability. She stopped calling him "Onii-chan" and doesn't quite look up to him and respect him the way she had before.

Nevertheless, the two of them are still very close. Rito always considers Mikan as his one and only precious little sister. And Mikan is happy taking care of Rito at home. Until Lala's arrival, it was still only the two siblings together at home, and at one point, she felt a little lonely from not spending time with Rito lately. Her friends believe that the reason she rejects many interested boys at school is because she already has a "wonderful Onii-chan". Their impression comes from the fact that Mikan talks about Rito a lot at school, despite mostly calling him a useless big brother who's nothing really great.

Even though she says that he's only good at useless things (which was shown a couple of times in the series), Rito has proven to be useful at more life-threatening situations, and that he can be counted on when someone is in trouble.

Lala Satalin Deviluke
Similar to how she treats her older brother, Mikan generally acts like an older sister to the childlike Lala. Mikan is somehow extremely casual and unfazed with the eccentricities around Lala, whether it's Rito's recent engagement to Lala, or even Lala's alien origins. Even finding Lala completely naked in Rito's bed has become a normal occurence to her. Mikan is pleased to know that things will get more interesting upon Lala's arrival in their lives.

Lala always enjoys Mikan's cooking.

Golden Darkness


Mikan is Yami's most significant relationship. Perhaps due to appearing to be the same age, Mikan constantly approaches Yami to encourage a friendship with her. Although Yami was hesitant at first to be aquainted and friendly with anybody, she has also grown attached to Mikan. They are often seen hanging together. Mikan is essentially the only person Yami truly considers as a friend, and has become willing to put her own life at risk to protect her.

Momo Velia Deviluke
Although she at first welcomed Lala's little sisters into her home, Mikan and Momo's relationship has grown humorously adversarial when Rito is involved. Strangely, while she doesn't mind the innocent and childish Lala clinging onto Rito and sleeping naked next to him, Mikan has a particular dislike of Momo's more mature doting and more sexual advances with Rito. Although it's not explicitly stated why, it could be because she is somewhat suspicious of the mischievous Momo's intentions. Or more likely it is due to feeling that, unlike Lala, Momo is gradually filling the place in Rito's life which belonged to Mikan. This is how Mikan felt when she reflected on how Momo helps her with the cooking and laundry at home, gradually taking the wife-like position in Rito's life, which had always been occupied by Mikan. But Momo assures her that this was not the case, and that Rito himself expressed how precious Mikan is to him as his little sister. Unknown to Mikan, Momo is adding her to the "Harem Plan," intending to include her into the harem Momo is building around Rito, despite Mikan being Rito's sister.

Nevertheless, Mikan has become something of an obstacle to Momo, barring Momo's access to Rito and warning Rito to be careful around Momo. She now acts as a sort of sentry to stop Momo from sneaking into Rito's bed at night. She even becomes uneasy when she is forced to leave Rito and Momo alone together at home, as, after being untimely distracted, she rushes straight home to prevent Momo from doing anything to Rito.

Classmates and Teacher
Mikan is often praised by those who know her at school, such as her friends and her teacher. She is seen to have at least two female friends at school, but no male friends because they all would like to date her, which she is not interested in.

Her friends praise her for being cute, talented and popular. They are also interested in her love life, as she is quite popular with the boys, but continually rejects their invitations on dates because she is apparently not interested in dating. Because this effectively makes her older brother, Rito, the only boy in her life, and because she apparently talks about him at school, her friends believe that Rito must be a very cool big brother to her and are eager to meet him, which Mikan always dodges from allowing to happen.

Mikan's teacher, Haruko Nitta, is a big fan of Mikan's mangaka father's work, and may have planned a home visit to Mikan's house with the intention to meet him. Rito has said that because Mikan is so mature and reliable, everyone at school, perhaps including her teacher, depend on her.

Trivia

 * According to a "Full size Dakimakura Cover-Mikan Version", her BWH measurements are 70-52-73.
 * Like many other anime girls (and some guys), Mikan entered Saimoe Contests.
 * ​To see her result, visit here: http://saimoe.wikia.com/wiki/Yuuki_Mikan
 * To vote for her when the match is on, visit here:  http://www.internationalsaimoe.com/voting/
 * Mikan's cameo appearance with Celine in chapter 1 page 37 in the manga Mayoi Neko Overrun!



And again in chapter 3 with her friends in page 26.

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And again in chapter 6.