Takao Hiyama

Takao Hiyama (also known as the Third diary owner) is a character in Future Diary (Mirai Nikki). He serves as the homeroom teacher (often for math or similar subjects) at the school attended by protagonists Yukiteru Amano and Yuno Gasai, appearing as a somewhat strict but occasionally friendly adult in his thirties.

In reality, he leads a double life as a serial killer targeting defenseless women, using a large knife or machete. He possesses the Murder Diary, which predicts the time, place, and circumstances of his future killings, allowing him to plan them with precision.

His role is prominent early in the series as one of the first major antagonists Yukiteru encounters in the survival game. Little else is shown of his deeper personality due to his relatively short screen time.