Sayaka is Madoka's classmate and best friend, a second-year at Madoka's school. She is a lively tomboy with strong ideals of love and lawfulness. After helping Madoka rescue Kyubey, she contracts with him to grant her wish to heal the wounded hand of Kyosuke Kamijo, a young violinist that she is infatuated with, visiting him daily in the hospital.
As a magical girl, Sayaka's weapon of choice is a cutlass, being able to produce multiples of them at a time. She also has an extraordinary regenerative ability due to the healing nature of her wish. Sayaka insists that her wish is selfless and feels that fighting witches to save people is a bonus, even after witnessing Mami's death. As Sayaka's ideals are put against the reality of her wish's consequences and the stress of fighting, her view of the world is slowly corrupted. She becomes hateful and distrustful towards others, including Madoka, whom she lashes out at and accuses of being selfish.
After learning that her soul is no longer in her body, but in her soul gem, Sayaka starts to believe she is a zombie; and when her friend Hitomi confesses to her about her love of Kyosuke, Sayaka falls into isolation and refuses all help. In her despair, she loses faith in humanity and justice, making her give up on her ideals and herself; thus leading to her soul gem becoming fully corrupted, turning into a grief seed, making her into the witch known as Oktavia von Seckendorff the mermaid witch, an armored mermaid witch with her barrier resembling a concert hall, where a figure similar to Kyosuke is playing among faceless figures. Though Kyoko and Madoka attempt to communicate with her, they realize that they can't do anything to save Sayaka. Kyoko then performs a powerful attack to finish off Oktavia, taking her life along with the witch's.
Despite Madoka's reworking of the world in the final timeline, Sayaka still makes a wish in the new world, and thus ends up disappearing after exhausting her soul gem. Despite this, however, Sayaka does not regret her wish, and hopes that Hitomi will make Kyosuke happy, before leaving with Madoka to the afterlife.
