Nodame Cantabile Wiki
Chiaki's former girlfriend. Coming from a wealthy family, she majors in singing (more specifically opera). She is the "belle" of the school due to her looks and voice. But she's in a constant dilema for losing to Suganuma Saya all the time.

Despite breaking up with Chiaki and Saiko has been in love with him all along. She broke up with him because when it came to music, he was equally critical of everyone including her, and yet even though he was far more talented than everyone (and herself), he was the most critical of himself, and that made it hard being with him. After breaking up with Chiaki she goes through a few relationships, but because of her lingering attraction to Chiaki, is never able to fully put him behind her.

Later on, she comes to terms with the fact that Chiaki has moved on without her, and presumably moves on as well.
Saiko sometimes exhibits a spiteful streak in her, especially to those whom she views as rivals, but is also capable of gentleness. Once, when a drunken Nodame bumped into Saiko at a karaoke restroom, Saiko first smacks her away, then after realizing Nodame was drunk, gave Nodame her shawl before leaving.