Rin is a perceptive, serious, resourceful and very competitive person. Though she is widely admired at school as a prim and proper honor student, it is a front she puts up in order to prevent others from prying into her life. In private, she is notably loud, shrewd, stingy and bossy, but usually means well for those she cares about. She is known as a model student and idol of her school. Her manner of speech is often hostile and dismissive of other people, but deep down she has a caring, big-sisterly disposition. Her tendency of making trivial mistakes at the worst possible moment is a hereditary curse. Though she really is a lot nicer than she seems, she claims to always make her decisions based on cold, rational logic in the end. In her own words, it's "not a very cute personality". In fact, her choice in personal clothes is probably an overreaction to that.[5] Despite claiming that she would do anything in order to win the Holy Grail War, no matter how underhanded, she has a deeply rooted sense of honor, seen refusing to dispose of Shirou despite numerous easy chances of doing so, simply because she owes him and deem disposing of him without clearing her debts to be cheap.

During her childhood, she understood the Fourth Holy Grail War about as much as Shirou understands the Fifth, seemingly understanding while not actually comprehending it. She saw her father as a great magus who must be respected and loved, but failed to understand the negative aspect of his personality, the coldheartedness that accompanied such an ideal. If he had lived until Rin could actually understand his personality, it is likely that it would have greatly affected the development of her own personality. It is unknown if she would have opposed such inhumanity and left the path of a magus, or if she would have become a “perfect and coldhearted” magus like her father. Either fate for Rin would have been one far away from happiness.[6] Due to Tokiomi's early and untimely death, she was not aware of the original goal of the Holy Grail War to open a “hole” beyond the World.[7]

For the sake of her deceased father and her family's name, Rin seeks to obtain the Holy Grail, though she has little personal desire for it. Unbeknownst to her sister Sakura, Rin feels guilty and believes that she has abandoned Sakura after she is adopted into the Matou household, so much the guilt was what driven her to revive Shirou, Sakura's target of affection, at the brink of death. While Rin eventually admits that she has always watched Sakura from afar, she never realized how much Sakura suffered under the Matou and fooled herself into thinking Sakura was happy to alleviate her own guilt.