Rin Tohsaka

Rin Tohsaka

Rin is a model student and idol of Shirō's school. She barely talks to other students in her school and exhibits a desire to be left alone, as exemplified by her tendency to stay on the school's rooftop, away from the rest of the students. She is also secretly a magus, and a Master in the Holy Grail War. Rin is reared as the successor to her family's magecraft, instructed by her father, Tokiomi Tōsaka, to prioritize sorcery over her own interests. After her father is killed, Rin continues to perfect her sorcery, with some guidance from Kirei Kotomine. She strives to earn the admiration of her peers to avoid drawing attention to her private life, even though she is secretly stingy, tomboyish, and a slacker. She is perceptive, resourceful and avidly competitive. Although she tries to summon a Saber-class Servant, she accidentally calls Archer instead.

Rin excels in transformation of energy, which includes storage of Mana in objects. She stores all of her mana in jewels that she charges daily to bypass her body's natural limitations on releasing energy. She can detonate her jewels on contact with an object, resulting in a release of energy equivalent to an attack rank of "A". Her most common offensive spell is "Gandr", which fires concentrated mana in the form of a black orb from her finger. On contact, the spell amplifies physical conditions -- a person who is already sick, for example, becomes far sicker upon being hit. Rin is also proficient with reinforcement sorcery, which she uses on her legs to give herself more speed.

Fate/stay night

By the conclusion of the prologue, Rin would have used two Command Seals on Archer; the first is to force him into submission after he acts insubordinate to her briefly after he is summoned, and the second is to force him into ethereal form before he is killed by Saber. In all scenarios, her position as narrator is replaced by Shirou.
In Fate, Rin acts as an advisor to Shirou, dutifully attempting to school him in traditional sorcery in light of his powerful Servant, Saber. Although Shirou's recklessness results in the death of Archer, she bears Shirou no ill-will, though she hides bitterness at her loss of both her Servant and her chance at winning the war. Rin is later stabbed by Kotomine Kirei in Shirou's home, though she survives and ultimately leaves for London at the war's end to become a true magus.
Rin is the heroine in "Unlimited Blade Works" scenario, and has a romantic relationship with Shirou. In "Heaven's Feel" scenario, she uses the Jeweled Sword Zelretch to fight Matou Sakura.
Rin and Shirou become partners in every scenario. In fact, Rin does care for Shiro. However, aside from her heroine scenario, UBW, in which she ends the 5th Grail War while continuing some romantic interest with Shiro. Their relationship is still placed secondary to her desire to join the Association but she asks if Shiro would be willing to travel with her to London as her apprentice so they can stay together and she can watch over him. In Fate scenario, she becomes only an observer of Shiro's life and continues her friendship with Shiro after Saber's departure. In Heaven's Feel, she does not pursue her feelings further because of Matou Sakura, her biological sister, who is in love with Shiro. She thus puts her feelings aside in consideration for her sister whom she felt she abandoned

Fate/hollow ataraxia

Rin also appears in Fate/stay night's sequel, Fate/hollow ataraxia, when she wields the Kaleidostick, another of Zeltretch's inventions, which when activated transfers knowledge from an alternate version of its user into its current wielder, in addition to providing an ample source of Mana. However, the Kaleidostick dislikes its creator, and frequently manipulates its user into humiliating situations. In Fate/hollow ataraxia, the Kaleidostick is responsible for transforming Rin into the magical girl Kaleido-Ruby. Also Rin's rival from Clock Tower, Luviagelita Edelfelt is introduced.
At the night of the final loop, Rin guards the Fuyuki bridge with her servant, Archer, from a horde of "monsters" to prevent them from chasing after Shiro/Avenger.

Trivia

- It is possible that Rin is a descendant of vampires because of her connection to Zelretch. It is alluded and implied by Kotomine when he mentions that The Tohsaka house is built atop of a vampire's leyline, and that burying Tohsaka in the earth could do good for her mana, as vampires can sleep under the earth to recover their strength.