Base

The Base (ベース, Bēsu) also known as Murder Model and/or alter ego refers to personality belonging to prisoners of Haguro Prison, which is believed to be affected by mirror neuron. As the prisoners of Haguro Prison are normal girls by day, they turned into serial killers by night, distinctly whenever the 'murder experiment' occurs. The girls also tend to have similar habits to those of their murder model, for instance Karen Kirishima's masochism to which based on her murder model, Albert Fish. It's later revealed that not only girls are affected by the Medusa Syndrome, but boys too, allowing them to develop their Murder Model. While some needed to inherit other's murder model after its user die, a murder model can also be used by multiple users at the same time.

Bases

 * Sayoko Onigahara - Josef Mengele
 * Seri Dojima - Gary Lewingdon
 * Maki Dojima - Thaddeus Lewingdon
 * Chika Amagi - Henry Lee Lucas
 * Karen Kirishima - Albert Fish
 * Aya Tomoe - Mutsuo Toi
 * Shion Magaki† - Albert DeSalvo (inherited by Kiriko)
 * Kiriko Makimura - Albert DeSalvo
 * Katya Rastorgueva - Andrei Chikatilo
 * Miina Isurugi - John Wayne Gacy
 * Yoko Kuroki - Arthur Shawcross
 * Mao Futaba - Jack the Ripper
 * Rein Saionji - Richard Chase

Trivia

 * Among those in the Haguro Prison, Yoko is the last to have her murder model revealed. She was also the first one to experience the Medusa Syndrome.