Takao Hiyama

Takao Hiyama (火山 高夫, Hiyama Takao) is the Third diary owner. Ostensibly the homeroom teacher of Yukiteru Amano and Yuno Gasai, Hiyama moonlights as a serial killer, hunting down defenseless women and killing them with a large knife or machete. He owns the "Murder Diary".

Appearance and Personality
Hiyama is a man of about thirty, with long red hair, tied in a little ponytail, and green eyes.

Little of Hiyama's personality is revealed during his short time in the story, but as a teacher he enjoys dropping surprise English tests on his students. He seems to be quite strict, although sometimes is friendly with his students, as was shown in the scene where he allows Yuno to make her clay model of Muru Muru, though likely only because she claimed it was a brain exercise.

In fact, he was a very manipulative and sadistic man; he told his students to be careful of a serial killer despite being the culprit. Hiyama is also shown to be very paranoid, as he destroyed his Future Diary twice when Muru Muru first introduced it to him. Despite being told otherwise, he still believed that she was recording his crime in the diary believing it to instead be evidence of his criminal past. Because of his paranoid nature, Muru Muru predicted he would be the first Diary holder to be killed; this was later proven.

Hiyama's Future Diary is the "Murder Diary", which predicts the future of his victims. It tells Hiyama how and where he will kill his next victim, and how best to corner and kill them. Due to the nature of the Survival game, the other diary owners are treated as victims, allowing Hiyama to easily track them down. However, his diary does not provide any information beyond that, leaving him unable to predict the movements of other people or how his victim may try to defend themselves against him.

As a serial killer, Hiyama wears a hat, gas mask with goggles and a bulletproof and apparently explosive proof jacket. This makes him impervious to almost anything that would try to hit him. His trademark weapon is a large machete-like knife.

He is shown to have many weaknesses, two of which being his paranoid demeanor and how he merely corners his victims and cuts them down with his knife. Hiyama is not as powerful as many of the other diary users, primarily because his diary doesn't show him how to defend against his potential victims' retaliation. This has been exploited several times across the series.

This makes him the weakest of the participants, which Muru Muru reinforces by believing he would be the first participant to be eliminated from the Survival Game.

The Survival Game
Takao Hiyama was a killer at least two years prior to the events of the Survival Game. He appears in the first episode, warning the students in his class, Yuno and Yukiteru among them, to be careful of the serial killer, even though he was the serial killer himself, evidenced by him having stalked a woman and later murdered her that very night.

Muru Muru appeared and presented him his Future Diary, but with as paranoid as Hiyama was shown to be, it took three attempts for him to realize it recorded his future and that Muru Muru was not recording the crime he committed.

The following day Hiyama realized that Yukiteru was a Diary owner as well after having aced the math test using the results shown on his Future Diary. Hiyama also encountered another Diary owner at the old art university the same day, 9th, Minene Uryu, however Minene fled from him to join forces with Masumi Nishijima to escape him.

Later Hiyama is shown to target Yukiteru and follows him to a building, unaware that Yuno was helping Yukiteru escape his death. As Hiyama reaches the roof, he is unable to find both Yukiteru and Yuno, and he quickly pulls out his diary to locate his targets. Yuno then runs out to distract Hiyama, and as Yukiteru leaps up from his hiding place, he tosses one of his throwing darts to shatter Hiyama's diary. Hiyama is quickly erased from existence, much to the surprise of Yukiteru. Because of this incident, the other Diary Holders mistakenly believe Yukiteru to be the most dangerous of the group, prompting them to target him.

The Final Battle
Hiyama is reborn towards the end of the story when Yuno, Muru Muru, Yukiteru and Minene jump back in time to the third world, where he is shown to be murdering a woman. He witnesses the explosions occurring at Sakurami Elementary School, thus allowing one of his potential victims an escape while he is enthralled with the sight. He then continues his rampage only to be tackled by Yomotsu Hirasaka. Two years later, he is shown to still be a criminal and on the run from the authorities. In the anime, Hiyama is captured by Yomotsu and is seen in prison; Yomotsu appears to visit him regularly, much to Hiyama's annoyance, although he does not seem to bear any sort of grudge.

Future Diary: Paradox
Hiyama also appears in the spin-off Future Diary: Paradox, stabbing Yukiteru after Muru Muru accidentally destroyed the intended timeline by killing Yuno. Aru Akise saves Yuki and takes his place in the survival game, Hiyama trying to kill him but ends up stabbing a fusebox with his machete, electrocuting himself to death. However, he is resurrected by Muru Muru to restart the game, but the events of Paradox are erased, leading to his death yet again.

Trivia

 * Hiyama is named after Vulcan, the Roman god of fire and volcanoes.
 * Hiyama's character theme song is "THIRD/Antares Cr302" by Aki Hata.
 * He is the first diary holder to die, both before and after the Survival Game began.
 * He died a total of three times before the Survival Game started.
 * In the anime, he accidentally destroyed his diary attempting to attack Muru Muru, who resurrects him. When she reveals that she knows about his diary he destroys it for a second time, killing him yet again.