Personality and background
Yuki is depicted as an attractive, reserved, and accomplished young man with many admirers, but who finds being friendly difficult. As a young man possessed by the rat, the animal that according to legend was first to arrive at the initial zodiac banquet, Yuki is talented at anything he tries (except cooking). However, when Yuki was young, Akito Sohma kept him isolated from the rest of the family and convinced him no one liked or needed him; because of this emotional abuse, Yuki has low self-esteem and feels isolated. He is known as "Prince Yuki" and "Prince Charming" at school, where despite his popularity he must avoid intimacy with girls lest they trigger his transformation into a rat. He has a fan club headed by Motoko Minagawa that tries to "protect" him from other admirers, with the result that Yuki is further isolated. Yuki, however, wishes that he could be with people as friends, rather than be admired from afar, and envies both Kyo Sohma's and Kakeru Manabe's easy ways with others. He is touched when, faced with the prospect of having her memory of the Sohma family secret erased, Tohru Honda asks that he remain her friend, which no one had asked him before.
With Tohru's help Yuki is gradually able to "open the lid" on his feelings, and the summer after she begins living in Shigure's house, Yuki admits to himself that he loves her. In volume 14, he realizes he does not see her as a woman the way Kyo does, but as a mother figure. This is possibly a result of his distant relationship with his real mother (see below). Eventually, he falls in love with fellow student council member Machi Kuragi, who accepts him completely (even Tohru saw him as a prince, while Machi did not; when another council member commented on his princehood, she replied that he was not at all like a prince, and walked away.) However, in the anime, Yuki's relationship with Tohru is defined to more romantic and portrays, like Kyo's, a relationship that sees Tohru as a potential romantic companion.
As a child, Yuki was traumatized by Akito Sohma, the leader of the Sohma family. When Yuki was younger, Akito used to have total control over him. She would tell him terrible things that he could never forget, like that he was the most hated member of the family, and that if it weren't for her, Yuki would have no reason to exist. These statements were seemingly confirmed by the behavior of the rest of the family: Hatsuharu proclaimed he hated Yuki (although he later comes to adore Yuki), despite the fact he had never met him before. His brother, Ayame Sohma, brushed off his cry for help, and Kyo always hated and blamed him. Everyone else in the zodiac did not speak with him, though that was probably not an intentional snub on their part. On top of being mentally abusive, Akito was often physically abusive as well, and sometimes would lock Yuki away inside a dark room to torment him. As a result of the combined abuse, Yuki has terribly low self-esteem, and suffers from self-hatred and an inferiority complex. Though his outward demeanor shows nothing of his childhood torture, Yuki reveals to Tohru that he does not care or appreciate who he is as his personality was shaped to please others and conform to society, which he incidentally excels at.
Yuki's worst enemy would be Kyo Sohma, the cat of the zodiac. Hatsuharu Sohma felt animosity towards Yuki during part of their childhood because of the story often told to Haru about the rat taking advantage of the stupid cow; this made Haru develop an inferiority complex towards his older cousin. However, after actually meeting Yuki face-to-face, Haru was able to see Yuki's extreme kindness and developed a deep admiration for him.
Yuki also feels a close connection with his cousin Kisa Sohma, as Kisa was teased because the children in her class thought she was different from others. Until Tohru Honda touched her heart, she didn't go to school and she couldn't speak, much like Yuki back when he was younger. Likewise Yuki, despite his popularity, rarely interacted with anyone on a personal level and was extremely private and introverted. Until he met Tohru, Yuki was afraid of becoming close to anyone because of an incident during his childhood when his secret was discovered by his friends during a game of tag, when Akito ordered Hatori Sohma to erase the children's memories, thus leaving Yuki alone and without friends. After meeting Tohru, Yuki started warming up to other people and becomes much more social, as well as accepting who he really is.
Yuki also appears to have respiratory problems, due to his weak bronchial tubes, and gets regular checkups from Hatori to monitor his condition. In his childhood these asthma attacks were apparently frequent, though they appear to be less so in the present. Still, he has to take extra precautions because he occasionally has attacks, which could cause him to transform in public. Throughout the manga, the attacks are less and less frequent.
After Kyo was freed from the curse, a series of events was triggered and the rest of the cursed Sohma family members became free. Yuki is the last Sohma member to be freed, noticing this as he was talking to Machi. The spirit of the zodiac took the rat spirit and thanked Yuki for keeping his promise for a long time. It is possible perhaps Yuki was the last one to be freed because he was the rat, the first of the Jyuunishi.
Relationship with Tohru
While in the manga, Yuki reveals feelings toward Tohru as those of love towards a mother, the anime focuses on the relationship in a more romantic light. Yuki is shown to have noticed what type of a person Tohru was before she actually came to live in Shigure's house. Yuki is startled at her innocence and ability to constantly love and be happy, and is quite overprotective of her. He holds great trust in Tohru who is able to awaken Yuki's desires to be himself and helps him admit his inner insecurities. Although Tohru is able to understand Yuki to a great depth and shares mutual feelings of happiness and security around him, she also perceives his dual identity as a prince (though she doesn't confuse both sides). At the end of the anime, Yuki realizes how Tohru is precious to all the zodiac members and is necessary for Kyo's curse to be broken and helps her to reach out to him; however there is no definite conclusion in the end as to what happens in the future for either.
While reminiscing in Volume 15, it is revealed that Yuki had first met Tohru as a young girl. He had run away from the Sohma House, and eventually got lost. While continuing his walk, he saw Kyoko Honda surrounded by policemen and at first sight looked like she was crying. Yuki hid behind a pole and watched as Kyoko began to scream out the description of her daughter as an "adorable little girl with an adorable dress and adorable-looking pom-poms in her hair." Kyoko said that if she didn't find Tohru, she would "rain death on [the police's] miserable cursed soul," and started crying.
Yuki realized that there were some mothers who love their children that much, and then he recalled that in his haste to leave the Sohma House and get as far away as possible, he had in fact seen a girl; it was lost Tohru. Yuki backtracked and found Tohru, and was about to run back to Kyoko to tell her, but suddenly realized Tohru was following him. He decided to lead her back to her home, and when they had reached their destination, Yuki gave Tohru the hat he was wearing, which is later revealed to be the one he had gotten from Kyo some time before. He then transformed into a rat, (due to being weakened from having trouble breathing) and ran behind a corner to hide.
As Yuki watched Tohru and her mother reunite, he began to cry, because he was so grateful that he was able to help someone and feel needed at least once in his life. He also started to feel as though maybe the world was not as dark and hopeless as Akito told him it was.
In volume 10, Yuki confessed his love for Tohru, but later,in volume 14, it is revealed that he "was looking for a mother in her" and he always saw her more as a motherly figure; he confesses to a friend, Kakeru Manabe, that he was really confused about his feelings towards her because he felt it was weird the way he saw her as a 'mother' and he did not want to admit these feelings. Thus, he tried to approach Tohru in a girl/boy way, but he realized that he did not/could not love her that way because he tended to see her as a 'woman' complex. He also had started to come to the conclusion that Kyo was truly in love with Tohru (and vice versa) and he figured out that he would never be able to feel that way about her or look at her the way Kyo did, and resolved that he wanted Kyo and Tohru to be together because Kyo was the only one who would be able to make Tohru happy in that way.
After that, Yuki and Tohru were still friends, although, their relationship doesn't appear to be as deep, though it probably was. Yuki was trying to branch off from the Sohmas and Tohru, and Tohru was starting to fall more in love with Kyo. There is evidence of their relationship being deep, however, in chapter 136, where their hands are shown parting after Yuki finally tells Tohru how he feels about her (as a mother figure) and he calls her "Tohru" for the first time (as opposed to the usual "Honda-san") in their roughly three-year relationship.
Relationship with Akito
Yuki and Akito have a bitter past. Akito has been emotionally, physically, and mentally abusive towards Yuki; Yuki, as a result, was traumatized since then. In volume 15 it's revealed that, when Akito and Yuki were young children, Yuki was brought to the Main House to live with Akito. She kept him by her side at all times, seldom letting Yuki out of her sight. As Yuki recalled it, originally, Akito was kind and would only occasionally lose her temper. However, after Kureno's curse broke, Akito's world unraveled (since she had made the curse the basis of her existence), and she "snapped." Akito painted the walls of her room black, and also locked Yuki away in a dark room built "especially for [him]" for long periods of times.
Yuki once cried to his mother that Akito said "scary things"; Akito filled Yuki's head with terrible words, such as that he was the most hated of all the Zodiac children. Not only that, but she was slowly chipping away at his will, telling him the world was a black place and that there was no reason to hope and no possibilities to make his life better. She continued this day after day, until Yuki began thinking it was the truth. As a result, Yuki started to get very sick from the emotional strain, especially after Kyo's rejection of his friendship, which confirmed what Akito was telling him. Akito pretended that she wanted to comfort the ailing boy, but when he went into his room she merely taunted him by once again repeating how much he was hated, asking him if he was going to die, and calling him boring.
In chapter 95, Yuki attended the New Year's banquet, and told Akito that he forgave him for all he had done, because he simply wanted to move on with his life, unbound by the pain of the past. This instantly reminded Akito of the day Kureno's curse had broken, and thus, she reacted violently, hitting Yuki with a vase and wounding his face.
In chapter 132, Yuki learned of Akito's true gender. When asked by Tohru if it surprised him, Yuki responded that he couldn't explain what he thought of it all, since lately, so much had happened to him (such as the curse breaking).
Relationship with Kyo
Originally, Yuki did not hate Kyo; he actually wanted to be friends with him. But Kyo refused, as he hated Yuki simply for being the sneaky, conniving Rat. When they first met, Yuki wandered away from the Sohma house and found Kyo, lingering in the snow. He had first thought to comment about Kyo's hair, which he quoted in his head "Pretty Orange", but Kyo intervened before he could say anything, asking if he was the Rat. When Yuki confirmed, Kyo declared his hatred to Yuki hotly, before running off. His second meeting with Kyo first started when Kyo dropped his red hat. Yuki picked it up and offered it to him, but Kyo turned the hat down, saying that if the rat touched the hat, it wasn't his anymore.
The hat ended up in the hands of Tohru, who had gotten lost as a child. Yuki (whom Tohru did not recall nor recognize when they met again as teenagers) found her and led her home, giving her Kyo's hat as a 'good job' gift.
It has only very recently been revealed that Kyo never hated Yuki for who he was, but had been so miserable with his life that he felt he needed a scapegoat for all his misfortune. Kyo felt it would only be logical for the Cat to blame the Rat and began to hate Yuki for this reason alone.
Their relationship has become more overly complex since this revelation. Kyo has always felt Yuki was more fortunate and always able to take advantage of a situation like one should, thus Kyo's dislike of Yuki stemmed from envy. However, Yuki reveals to Kyo that he is jealous of Kyo, because despite all of Kyo's bad luck and misfortunes, he is not passive like Yuki (something Yuki despises of himself) and able to comfortably express his own emotions and thoughts verbally, regardless of what they are. When they both confess to each other, Yuki is further upset because Kyo, as usual, was able to confess first. In addition, Yuki knows he can never love Tohru or be loved by Tohru in the same way that Kyo can. At the very end of the last volume in the last chapter of the manga, Kyo and Yuki smile while walking past each other, friendly calling each other the usual "stupid cat," "damn rat."
Relationship with Ayame
When their relationship is first introduced Yuki shows downright hatred for his brother, ordering Shigure to skin Ayame's snake-form after he is first found inside Tohru's dress, even when it is later revealed that Ayame was merely doing this to stay warm as a result of being cold blooded. The two had a strained relationship since Yuki's childhood (they are ten years apart); Ayame tells Tohru that because of his brother's poor health, Yuki and he would often be separated for long periods of time, to the point Ayame almost forgot he had a younger brother. The rift between the two was cemented when a young Yuki tried to reach out to Ayame after Akito's mistreatment, but Ayame merely responded by pulling away, unable to understand Yuki's motives.
With prompting from Tohru, Yuki attempts to learn about his brother by visiting his store, which despite resulting in a large amount of disgust and shock from Yuki gives the brothers time to be honest with each other, even if that translated to an argument between the two. After Ayame's dramatic entrance during Yuki's parent-teacher conference with his domineering mother, in which he gives Yuki the confidence to reject his mother's control, the relationship between the two seems to improve greatly. Towards the end of the manga, Ayame offers to apartment-hunt for Yuki and be his guarantor, which Yuki accepts, even if it is slightly nervously.
Relationship with Mother
The fact that both Ayame and Yuki are members of the Jyunishi is quite unusual since it is very rare that any of the Jyunishi are siblings at any given time. Because their mother, who is only featured in the manga, was unable to force Ayame to bend to her will, she turned to Yuki and controlled every aspect of his life, including which schools he went to and what he would do after high school in college. Yuki became both emotionally fragile and detached in her attempts to gain status and wealth within the family while she bluntly and tactlessly shot down any attempts he made to refuse her wishes. This changes during a parent-teacher conference in which his mother gave him no say in his future, prompting Yuki to finally refuse her attempts after Ayame burst in dramatically and gave Yuki the confidence to stand up for his own ideals and dreams. Before Ayame's arrival, Yuki's mother countered Yuki's demands for a voice in deciding his future by claiming that he "never had a worthwhile thought in his life" and in his head, Yuki remembered how all his life, his mother refused to let words get to her and let them die, which is why he believed in not putting his own emotions into words. Later in the manga, Yuki asked his mother for a cell phone, the first attempt at making a better relationship with her, and she obliged by signing the paper he needed. She also tells him "Don't...use it wastefully," causing Yuki to later laugh and think that that was the first time she said anything so motherly.