|Hair Color||Dark Purple|
She has long dark purple hair and gray eyes. San wears the school standard female uniform.
She seemed to be a girl with a boyish, serious, and mature personality. She is good friends with Kazue Satou.
San was a minor part of class 3-3, not taking part in discussions about countermeasures and rarely involved with Kouichi or Izumi's groups.
San was one of the students present when Mr Kubodera killed himself ( "Sphere Joint"), and was among those who fled the room in terror.
Nonetheless, San decided to go on the class trip, willing to risk her life to break the curse; she shared a room with Yumi Ogura at the inn. San was among the students who heard Takako's broadcast ("Makeup"), and left the room along with with Yumi. She was horrified when her roommate attacked Kouichi, but still caught her when he and Mei knocked her over while escaping. Unlike Yumi, San did not pursue the duo, instead attempting to escape the burning inn. In "Stand By Oneself," San, who had met up with Sayuri, Yukito, and Kenzou previously, was making a run for the exit when a chandelier came loose and pinned her and the others to the floor. Kenzou, who was the least incapacitated, managed to free himself, but abandoned the others, only to be killed when a pillar collapsed on him just before he could escape.
While it is not explained how, it is assumed she was among the students saved from the burning inn by Chibiki, though San was knocked unconscious by the chandelier, as she was seen when the other survivors gathered outside the inn, she is shown inside Chibiki's car, being watched by the others, this is her last shown appearance as she is not shown with the group who visited Manabu in the hospital.
- She is ranked B in Another characters ranking.
- Her home address is 3-14 Asamida Yomiyama City.
- Her first name, San, means "sun," Watanabe means "cross over the border."
- Her name means "the sun that crosses over the border."