An in-depth look at Rin's personality.

Little is known about Rin by the time she first appears in Fruits Basket. When she first appears, she's in a hospital and has recently broken up with Hatsuharu. She seems to have suffered a great injury but despite her medical condition, she displays much ferocity in her attitude. It takes some time before we begin to learn about the reasons behind her actions.
When Rin was born, it seemed as if her parents loved her dearly. They spent a lot of time together and seemed like a very happy family until Rin asked a simple question: why was it that her parents were happy all the time, was there nothing to be sad about? The moment that the words came out of her mouth, Rin's life changed. Her parents, unable to keep up the charade any longer, snapped. Considering Rin to be ungrateful and disgusting, they began to treat her poorly, subjecting her to mental and physical abuse.

Eventually, even the abuse became too much for her parents and they kicked her out of their house. Rin was left to wander the streets alone until she collapses from weakness. Hatsuharu luckily stumbles across her and quickly summons Kazuma to help bring her to the hospital.

When she's recovering, Rin's mother pays her a visit while Kazuma and Hatsuharu are present. She tells Rin not to bother coming home as she can't bother to try loving her anymore and disowns her daughter in front of the other two Sohmas. Hatsuharu is shocked and furious, speaking up on Rin's behalf, calling her mother irresponsible. Although Rin is traumatized by her mother's actions, she's deeply moved by Haru's outburst.

For a child who experiences such love and happiness from her parents for the majority of her childhood, it's extremely traumatizing to have it all taken away from her. Rin, young and impressionable, believes that it's her fault that her parents have changed and expresses feelings of guilt. She carries these feelings with her throughout her teenage years.

Once abandoned by her parents, Kagura's mother invites Rin to live with them. Kagura and her mother have a very loving relationship which only acts as a reminder to Rin of the life she once had. Seeing the love between mother and daughter during meal times and other social moments becomes so painful and unbearable to Rin that she begins to spend all of her time in her room. Eventually, she sinks into such a deep depression that she's barely able to function. She rarely goes to school, has no friends and dwells on her negative feelings of guilt, anger and sadness.

The only escape from her darkness is whenever Hatsuharu comes to visit her. He takes her mind off her painful emotions and she's able to smile and be happy. They gradually fall in love with one another and when Haru wants to take their relationship to the next level, Rin is hesitant because she knows that Akito frowns upon such things. The alternative of Haru being with someone else is enough to drive her to ignore her hesitations and they two begin dating.

It isn't long before Akito finds out about Rin's relationship with Haru. When confronted about it, Rin is terrified that Haru will get hurt so she confesses that she's the one who instigated the relationship. This is exactly what Akito wants to hear and begins to berate Rin, echoing the horrible things her mother said to her. Akito's wrath escalates and Rin is pushed out of a second story window, sustaining a terrible injury to her back. As she lays bleeding, she thinks about how she wants to free Haru from the curse that ties him to Akito.

Akito's physical assault puts Rin in the hospital for months. During this time, she has plenty of opportunity to think about how she may free Haru. She decides her first course of action will be to break up with him so that he doesn't meet a similar --or worse-- fate. It's difficult for her but she's determined to cut ties with him while she looks for a way to break the curse.

No longer having Hatsuharu to lighten her mood, depression begins to take over Rin once again. She's forced into a solitary lifestyle where she skips school and often doesn't return home at night. Her classmates know little about her and find it hard to believe she has any friends outside school at all. They're quick to belittle her, feeling that her absenteeism is a result of a lavish lifestyle. This suits Rin, however, as she can freely move to investigate the Sohma curse. Tohru cares about Rin and worries about her but Rin continues to push her away, not wanting her to become involved with Akito.

Every day is spent trying to figure out how to break the curse. She's so determined and preoccupied with it that she eventually falls apart completely when she comes to the realisation that there may not be a way to break it after all. She's so desperate at this point that she believes Ren when she tells her that in exchange for retrieving a small box from Akito's room, she'll tell her the means to break the curse. This illuminates exactly how desperate Rin has become: she would never throw caution to the wind when it comes to Akito. In fact, she actively avoids Akito out of fear and breaking into Akito's room is exactly the opposite of what she'd normally do.

Of course, Akito finds her and is so furious with her transgressions that she locks Rin away in the Cat's Room, a place of solitary confinement. Akito subjects Rin to months of physical and emotional abuse and Rin nearly loses all will to live; she stops eating and barely moves. No one has come to save her and no one has even noticed she was missing for months on end.

When Rin is rescued from the horrible fate that Akito subjected to her, the tables have begun to turn. Having learned that she was trying to break the curse, Hatsuharu confronts her about her actions. They reconcile and get back together. Rin also discovers that the curse has already begun to break on its own. She's finally able to stop her lonely journey and can begin to focus on healing the pain within her.

While all of the other juunishi appear to be able to forgive Akito and move forward in their lives, Rin is unable to. The things Akito did to her are beyond an apology to Rin and she struggles to understand how everyone else is able to look past the terrible things that Akito has done. While Rin ends up in a better place at the end of the series, she's unable to shed her grief entirely. Being surrounded by people who genuinely love her and care for her will be the key to allowing her to unlock the full potential of her life.