If you've seen Fate/Zero, you'll know that Sakura Matou is actually Rin Tohsaka's little sister that was adopted into the Matou family since the next heir refused to take his spot and other stuff. Sakura, on paper, was going to be the next heir of the Matou family, but that wasn't the plan for her, she was set to become the vessel for Zouken. During her "training" Zouken had gotten some of the pieces from the lesser grail, and fed it to his worms. Those worms were then implanted inside Sakura, draining her mana but feed on her carnal impulses. Shinji was studying aboard during the fourth holy grail war, but he returned afterwords. He bullied her but eventually grew to love and accept her. Those feelings were short lived, once Shinji found out that he wasn't to be the next heir, he turned on her and despised her like the rest of the Matou family and began raping her nightly. This all sets up the Heaven's Feel route as she takes front stage instead of the side role she did in the first two routes.


She is the true master of Rider, but gave command to her to Shinji so she didn't have to fight Rin or Shirou. She notices that Rin and Shirou becoming closer, she started to resent Rin, blaming her for all her pain and suffering. Zouken, dissatisfied with Shinjis performance, began a genocide against the other Servants with his servant, the true assassin for F/SN, and the premature form of Angra Mainyu, the secret 8th servant class, Avenger. (Avenger doesn't have a body, so it replicates the host.) It goes on to kill Archer and Lancer, absorbing Saber and Berserker. It then spits out Dark Saber and Berserker as assistants. Gilgamesh eventually confronts Avenger, impaling it with several of his noble phantasms, but it regenerates too fast and absorbs Gilgamesh. Shirou finds out that Sakura is apart of the war and abandons his ideals, his ideal of becoming a hero of justice, in order to protect her. This is when she thinks that she is the Avenger servant. She seeks out Zouken to force him to kill her, along the way Shinji tries blackmailing her into having sex with him, instantly kills him and fully becomes Avenger. She kidnaps Ilya, intending to use her for the grails core, but Ilya is saved by Shirou and Kotomine, Sakura kills Kotomine, absorbs the true assassin, and purges her body of Zouken's worms. Rin is able to go toe to toe with Avenger, but fails in killing her little sister due to her love. Rin hugs Sakura and continues to do so even after Sakura stabs her in confusion. She begins to suppress her malice, Avengers power, long enough for Shirou to use Caster's Rule Breaker to defeat Avenger while keeping Sakura safe.

Here's the fun part, two possible endings. Normal and True endings.

Normal; Shirou traces Excalibur and destroys the grail. He dies. Sakura refuses to accept his death, living in the Emiya house, waiting until he returns. She dies of old age and reunites with Shirou in the afterlife.

True Ending; Ilya intervenes, closes the gate, and performs the Heaven's Feel spell on Shirou to keep him alive, and destroy the grail. Avenger is killed and she is alive and safe. Due to becoming Avenger and having pieces of the grail inside her, she became connected to the root of magic, giving her near unlimited amount of mana. Akasha (Rider), Shirou and her begin living with her, Rider existing on Sakura's mana.

Shinji rapes Sakura and does so for years, Sakura becomes the secret servant class, Shinji attemps to blackmail Sakura into sex, Sakura kills him. Shirou abandons his ideals and falls in love with Sakura. Sakura is saved by Shirou (depending on choices, shirou either dies or moves in with sakura and rider)