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 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, while in his true supernatural form he has noticeably sharper features such as sharp ears, claw-like hands and shark-like teeth. He also has 4 additional limbs protruding from his lower back.

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

In 1969, he is shown to have all-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 sort-of-meek teacher in his disguise, he is actually sarcastic, mischievous and quite short-tempered. He's also shown to be quite sadistic, having fun in threatening and scaring Nene and Kou ― although he quickly stops following a light warning from Hanako.

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

Despite him saying that he only pretends to care about his students, being a supernatural that can only pretend to be human, he has been shown to actually care for them genuinely.

When asked why he makes his teacher persona so different than his actual personality as a supernatural, he answers that it's just 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, of the present as well as 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 does not have any plans on doing 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 in 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.