Sayaka Miki is a character from the anime Puella Magi Madoka Magica. She is Madoka's best friend, as well as a fellow magical girl. She is also the witch Octavia, a form she can control with ease. In Rebellion, she serves as a "personal secretary" to Madoka, bringing hope to all magical girls.
Sayaka Miki fell in love with a talented musician named Kyosuke Kamijo, whom she would always visit at the hospital to keep him company. Kyosuke fell into an accident that resulted in his not being able to play violin. Due to his suffering, Sayaka made a deal with Kyubei that in exchange for healing the boy's injured arm, she would become a magical girl and fight witches. However, despite Sayaka's initial excitement, when she realizes the truth about magical girls, she falls into depression, as she distances herself more and more from the idea of falling in love with Kyosuke. Later, when her friend, Hitomi, confesses to Kyosuke, a confession he accepts, Sayaka succumbs to despair and becomes the witch known as Oktavia von Seckendorff, the Mermaid Witch.
In Rebellion, Sayaka manages to move on from her childish crush on Kyosuke, and even calls him "Captain Oblivious" in regards to him putting his violin practices over his dates with Hitomi.