The Handsome Rat of the Sohmas
As a child, Yuki was abandoned by his parents to live with the head of the Sohma family, Akito, as they sought to benefit financially from his status as the rat of the Sohma family. Yuki regularly dealt with physical and mental abuse from Akito, until he made a deal with cousin Shigure to be able to leave the main Sohma house to be able to live with the sinister writer at his house.
Yuki was created as a major character for Natsuki Takaya's Fruits Basket manga series. To give Yuki's character an androgynous appearance, Natsuki designed Yuki to be able to wear Chinese-style clothing and have a distinguishing style from Kyo. He appears in the anime adaptation of Fruits Basket, being voiced by Aya Hisakawa in Japanese and Eric Vale in English.
Yuki stands at 171.3 centimeters (about '5'7") and weighs 53.9 kilograms (119 pounds). He has greyish-colored hair and eyes in the manga, while both sport a more purplish color in the anime. Yuki is normally seen dressed in collared and tight-forming clothes, with a preference for Chinese-style attire. He is 16 years old at the start of the series and being the Rat of the cursed Sohmas, Yuki will transform into a rat if hugged by a girl or becomes greatly weakened.
A friendly and polite young man on the surface, Yuki lacks self-esteem and has an inferiority complex. While Yuki does have the desire to make friends with others and distance himself from the Sohma family, he lacks the self-confidence to try becoming more than an acquaintance to others. His interactions with Tohru throughout the course of the series allow Yuki to slowly open up to others and gain greater self-confidence.
Like Kyo, Kagura, and Haru, Yuki was trained in the martial arts by Kazuma Sohma. He is adept enough where he can effortlessly best Haru and Kyo. He also suffers from frequent asthma attacks as a result of having weak bronchial tubes. Due to being the Rat of the Sohma family curse, Yuki is able to naturally attract mice and rats to him.
At school, Yuki was among the most popular students in school and was part of the school student council. However, he felt more like an acquaintance to others and tried to avoid contact with members of the female student body who confessed to him lest they learn of his family curse. Those days would change when Tohru became a part of Yuki's life as the girl's selfless and kind nature led him to develop greater self-confidence to befriend others. Over the course of the series, Yuki would eventually become president of the student council and slowly develop a relationship with fellow council member, Machi Kuragi. Upon learning of the family curse being broken near the end of the series, Yuki would start up a relationship with Machi.
Tohru recalled in her younger days meeting with a red-capped boy who had escorted her home when she was lost while fleeing from bullies. She had kept the cap given to her by the boy as a keepsake, remarking that it was the happiest moment she had in her life. Unknown to her, Yuki turned out to be the boy that had helped her that day as he escaped the confines of the main Sohma house on that fateful day.
Tohru and Yuki would develop a close bond with one another throughout much of the series, with Yuki greatly admiring the selfless and kind nature of her character. During their trip to the Sohma beach house, Yuki would admit to loving her as he kissed her forehead and cried on her shoulder upon having an encounter with Akito. However, Yuki would later admit that his feelings towards Tohru were more as a motherly figure due to the parental neglect he received from his own family as a child.
The two became somewhat distant later on as Yuki focused on student council duties and Tohru would seek a means of breaking the Sohma family curse due to her love for Kyo, though the two remained on friendly terms with each other. At the end of the manga, the two had a final conversation where Yuki would call Tohru by her first name and confessed how he truly felt towards her.
Kyo and Yuki had a rather hostile and envious relationship toward one another throughout the series. Kyo viewed Yuki as being born lucky as he was greatly admired by others around him and sought to beat his cousin in a fight to be accepted by other members of the Sohma family. Yuki thought of Kyo as a fool for wanting to try getting acceptance from the Sohmas, believing that he would have a much better chance at gaining acceptance from those outside the Sohma family as he was more expressive with his feelings than Yuki could ever be. The hostility between the two would gradually wane over the course of the series as such where the two would get on begrudgingly good terms with one another by the end of Fruits Basket.
Enduring physical and mental abuse from Akito as a child, Yuki still carried a great fear for the head of the Sohma family despite his desires of wanting to live a life away from the confines of the Sohma family.
As a child, Haru was often teased by members of the Sohma family for being the dumb cow of the zodiac who was fooled into letting the rat sneak into attending God's celebration to the animals of the zodiac. While not having met Yuki personally up to that point, Haru developed an inferiority complex towards his older cousin. After actually meeting Yuki face to face, Haru was able to see Yuki's extreme kindness and developed a deep admiration for him.
The relationship between these two brothers was a shaky one due to the strained relationship they had for years. Ayame had neglected Yuki during his time of need when the latter suffered from abuse by Akito. Later in life, Ayame would seek to reconcile his strained relationship with his younger brother. But the memories of neglect and Ayame's self-absorbed personality prevented Yuki from accepting his older brother's gestures of kindness. Over time though, the two would slowly reconnect with one another and the bond became strengthened as such where Yuki was grateful for Ayame making an intervention during their mother's attempt to control Yuki's life beyond high school.
While seemingly annoyed with Kakeru's personality seeming similar to Ayame, the two still form a friendship with one another during their involvement with the school student council.
Becoming Yuki's love interest for later volumes of Fruits Basket, he developed an attraction to his underclassman due to similar tragic pasts they had dealing with their families. Machi was one of the few students who knew of Yuki's imperfections and his understanding of her complicated family situation led the relationship between the two to gradually develop into a romantic one.