Masumi Nishijima is a non-diary owner who's allegience seems to change over-time. He is a detective who originally works under the supervision of Kurusu Keigo, also known as Fourth. He also proposes to Minene Uryuu.
He has light brown/dirty blonde hair and eyes, though fans mostly draw him with dirty blonde hair. He stands at the height of around 170-180 cm. He is a bit tall, especially in comparison to Minene Uryuu, who is depicted to be quite short.