Rin is a model student and idol of Shirou'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 secretly a Magus and a Master in the Fifth Holy Grail War. In the beginning of the anime, she summons Archer for her Servant, although she originally wanted to summon Saber. Rin is reared as the successor to her family's magecraft, instructed by her father Tokiomi Toosaka to prioritize sorcery over her own interests. Two centuries ago, the Toosaka House, in collaboration with the estates of Makiri and Einzbern, helped found the Fuyuki Holy Grail Wars. The land of Fuyuki City, which possessed the second greatest spiritual power in all Japan, was owned by Rin's ancestor, Nagato Toosaka; at the behest of the Einzberns, he provided his property as battleground for present and future wars. Nagato was a kirishitan, as well as a pupil of Zelretch; these titles gave him considerable influence in both the Mage's Association and the Church, allowing the Toosaka family to participate in the Holy Grail Wars, free from harassment by either organization. Rin was brought up as the successor to her family's magecraft, and was instructed by her father to prioritize magecraft over her own interests. Ten years ago, Tokiomi Toosaka was selected as a Master in the 4th Holy Grail War, and Rin was entrusted to take care of the Toosaka estate until his return. Her mother, Aoi Toosaka, was left in a debilitated state from the war, so her care was left to her guardian, Kirei Kotomine. After her father was killed, Rin continued to improve her sorcery with some guidance from Kirei Kotomine. To divert attention from her private life, Rin has diligently strived to earn the admiration of her peers, even though she is secretly stingy, tomboyish, and a slacker. The rights to the Toosaka lands were inherited by Aoi after Tokiomi's death, and subsequently inherited by Rin after Aoi's death. Kirei managed them as Rin's guardian, and because of his foolhardy and coarse management, the majority of profitable properties ended up in the hands of others. It is possible that he believed the wealth was bad for her upbringing due to following the principles of humility and poverty. Although Rin resents the sacrifices she has endured for the sake of tradition, she is fiercely competitive and eager to prove herself as a skilled and capable magus. She was immensely disappointed at summoning Archer and ended up in a quarrel with him; however, the duo soon reconciled, set aside their differences and quickly got along. (Source: Wikipedia)

The fifteen-year-old protagonist of the story, Rin is the son of Satan born from a human woman and is the inheritor of Satan's powers. Rin can tap into the power he has inherited from Satan through the use of a demon-slaying katana, called Kurikara or Koumaken. The sheath acts as a portal to Gehenna (the demon world) which when drawn returns Rin to his demon form. While in his human form, Rin exhibits a number of physical traits that are signs of his demonic nature, such as sharper-looking teeth, slightly pointed ears, and a black, fur tufted tail (which he keeps hidden in his shirt). As a demon, Rin gains two blue flames that float above his head, long, elf-like ears, and his eyes turn bright blue. In both forms Rin can almost control his destructive bright blue flames, the trademark sign of Satan. However, when he draws Kurikara, the magnitude of the flames dramatically increase and often leads to Rin being "consumed" by his own flames and losing his mind. Rin also has a demon Familiar Cat Sith, Kuro, who was initially Father Fujimoto's. He is surprisingly good with his hands, and his cooking repertoire includes all kinds of Japanese and Western foods (home cuisine). (Source: VIZ Media)