Mitsuko Souma (相馬 光子, Sōma Mitsuko?) is a fictional character in the novel Battle Royale and its manga and film adaptations. In the English language manga she is nicknamed Mitsu, Mi-chan and "Hardcore" Souma.

Mitsuko is the second most dangerous person on the island next to Kazuo Kiriyama. She killed a total of eight people. Mitsuko as a teenager is portrayed Kou Shibasaki in the film; the young Mitsuko in the flashback is played by Suzuka Tonegawa.

She was officially designated Shiroiwa Junior High School, 9th Grade, Class B, Girl #11. Mitsuko has blood type A.

Source: Wikipedia