The Third Diary user. Takao is a teacher at Yuki's school who is secretly a serial killer who wears a heavy bulletproof trenchcoat with a hat and mask that hides his identity. Takao's diary is the Murder Diary which gives him details on who his next victims are and where and how he kills them. While the diary helps him catch his victims and prevents them from escaping, it does not tell him what to do if his victims will fight back thus he can be easily defeated.
It is revealed by Muru Muru that Takao repeatedly accidentally killed himself when she was presenting him with his Future Diary. First was when he thought she was a witness to his recent killing and sliced the phone, and then thinking the phone was evidence, he destroyed it again. She admitted she suspected he would be the first to go because of his paranoid personality.