Shirou's childhood friend and adopted sister who serves as the true Master of Rider. Plagued by years of abuse and infested with Crest Worms, she is manipulated into becoming the vessel for the corrupted Holy Grail. Her journey from a passive victim to a corrupted force, and finally to redemption, forms the emotional core of the trilogy.
Shirou and Sakura develop a deep romantic bond, culminating in a physical relationship.
Rin and Sakura are biological sisters separated by adoption, creating a complex familial tie.
Sakura is under Kirei's medical care, relying on his expertise to manage her Crest Worm condition.