San Watanabe

San is a somewhat tanned girl of slightly above-average height. She has shoulder-length deep purple hair and green eyes.

As a student, she was only seen wearing the standard female uniform; however, she decided not to wear the vest in summer.

San is shown to be a mature, serious, and sociable girl who likes to spend time with her friend Kazue Satou, which is why the two are often seen together; she also seems to get along with Matsuko Arita and Haruka Etou. Despite this, San is willing to do whatever it takes to ensure her survival, even if it means murdering one of her classmates to end the calamity.

San was a minor member of Class 3-3, not taking part in discussions about countermeasures and rarely getting involved with Kōichi Sakakibara or Izumi Akazawa's groups.

San was one of the students present when Shoji Kubodera killed himself in "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 in "Makeup" and left the room along with Yumi. She was horrified when her roommate attacked Kōichi, 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 Kakinuma, Yukito Tsujii, and Kenzō Kawahori offscreen, was making a run for the exit when a chandelier came loose and landed on her and the others. Kenzō, 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 San was among the students saved from the burning inn by Tatsuji Chibiki, though she was knocked unconscious by the chandelier, as she was seen when the other survivors gathered outside the inn, inside Mr. 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 Maejima in the hospital. It is likely that, following their daughter's recovery, the Watanabe's pulled San from Yomiyama North and left town.

• The name San (珊) means "coral".

• San's surname, Watanabe, means "to cross the border," as well as being the fifth most common Japanese surname in and outside Japan.