Tsuchigomori

Tsuchigomori (土籠) is a teacher at Kamome Academy. He is secretly a supernatural, representing the academy's 5th School Mystery, the 4PM Bookstacks, and is also its curator.

Appearance
Tsuchigomori is a tall, lanky man. He has spiky black hair with long white fringes and purple eyes.

When he disguises himself as a human, he looks almost indistinguishable from any regular person. In his true supernatural form, he has noticeably sharper features such as sharp ears, claw-like hands and shark-like teeth; he also has four additional limbs protruding from his lower back.

He wears a white coat with a purple sweater underneath and golden eyeglasses.

In 1969, he is shown to have entirely black hair and doesn't wear glasses. His sweater is also replaced with a dress shirt.

Personality
While Tsuchigomori seems like a normal, caring and somewhat meek teacher in his human disguise, he is actually sarcastic, mischievous and quite short-tempered. He's also shown to be quite sadistic, having fun with threatening and scaring Nene and Kou ― although he quickly stops after a light warning from Hanako.

Although he is a teacher, he is shown to dislike children because of their noisy attitudes. Tsuchigomori also has an odd sense of humor and likes to joke around, such as saying that he likes to eat human children, only to be met with terrified looks in response.

Despite him claiming that he only pretends to care about his students, he has been shown to actually genuinely care about them on various occasions.

When asked why he makes his teacher persona so different than his actual personality as a supernatural, he answers that it's simply because he feels like it.

Number 5's Powers
As the curator of the 4PM Bookstacks, he has access to the entire body of knowledge surrounding the school, along with the present, past, and future. He seems to know everything about every student that has ever attended the school.

Even after his yorishiro and boundary were broken, his powers still allow him ways to retrieve the books in the library.

He mentions that because of his position, it's possible for him to alter the future, but he does not plan to do so because any curator who does will be erased from existence.

Trivia

 * His favorite snack is bekko candy.
 * His latest concern is how hard it is to live a double life as a teacher and a supernatural.
 * His name is a reference to the yōkai Tsuchigumo/Earth Spider (土蜘蛛) but with the phonetic 'go' (five) substituted in as a nod to his school mystery number.