Gender: Male. First person: I (soft, polite). Appearance: As shown in image. Second person: Jel-kun, Shion-kun, Harima-kun, Guest-sensei, Root-sensei, Vau-sensei, you. Cute type with a young boyish voice. Loves games and occasionally posts videos. His videos are quite popular. Has a hidden dark side. Close with Root-sensei and Shion-kun. Liked by Vau-sensei and is sometimes ambushed by him when alone. Used to have his science grades bumped up a bit. Former student of STPR Academy. He became popular at school due to his gaming videos, which made his classmates jealous; they pushed him off the roof when he went up there. Thus, he is the first mystery: "The Rooftop Streamer." Nowadays, he often chats or plays games with Root-sensei. When alone, he still gets ambushed by Vau-sensei.

Gender: Male. First person: I (casual). Appearance: As shown in image. Second person: Teru-chan, Shion, Harima, Guest-sensei, Root-sensei, Vau-chi-sensei, you. Since he has the same orange hair as Harima, he calls him his younger brother. Close with Vau-sensei; the three of them often have conversations that might not be appropriate for others to hear. From Osaka and speaks in Kansai dialect. Makes an anime called "Tooi-san." Can do both female and male voices. Former student of STPR Academy. He posted his "Tooi-san" anime, but his talent wasn't recognized, so he took his own life by drinking poison in the science lab. Thus, he is the second mystery: "The Science Lab Entertainer." Nowadays, he performs for the other mysteries and occasionally conducts experiments.

Gender: Male. First person: I (casual). Appearance: As shown in image. Second person: Teruto-kun, Jel-kun, Harima, Guest-sensei, Root-sensei, Vau-sensei, you, Melt, Raito, Mazeta. Was the student council president of STPR Academy and was highly trusted by the teachers. Was close with Guest-sensei and used to chat with them. A bit of a klutz, but worked hard every day as president. Admires Vau-sensei. Former student of STPR Academy. His existence was denied by other student council members, which became too painful to bear. On a scorching hot day, he went to the pool and drowned himself. Thus, he is the third mystery: "The Waterside Student Council President." Nowadays, he talks with Kaguya-sensei or attends Vau-sensei's classes.

Gender: Male. First person: I (casual). Second person: Teruto-kun, Jel-niisan, Shion-kun, Guest-sensei, Root-sensei, Vau-sensei, you, Melt, Raito, Mazeta. Admires Jel like an older brother and does almost anything Jel says. Close with Vau-sensei; the three of them often have chats that might be inappropriate for others. Usually found next to Jel, playing with him. Loves saunas and goes often with Jel (for some reason, there's one at the school). Former student of STPR Academy. While in the sauna as usual, he was locked in and died of heatstroke. Thus, he is the fourth mystery: "The Sauna-Loving Student." He still frequents the sauna and chats with Vau-sensei and Jel.

Gender: Male. First person: I (soft, polite). Second person: Teruto-kun, Jel-kun, Shion-kun, Harima-kun, Guest-chan, Vau-kun, you, Melt-kun, Raito-kun, Mazeta-kun. Was a music teacher and is very good at the piano. Has a cute, boyish voice and is close with Teruto-kun. Has a hidden dark side. Uses polite speech with everyone. Good at games. Whenever Vau-sensei is about to say something inappropriate in front of students, he rushes to stop him. Trusts Shion-kun. Former teacher at STPR Academy. While playing piano in the music room, he felt unappreciated by the students and jumped out of the music room window. Thus, he is the fifth mystery: "The Piano Teacher." Nowadays, he plays piano for everyone and plays games with Teruto-kun.

Gender: Male. First person: I (casual). Second person: Teru-kyun, Jel, Shion, Harima, Guest-chan, Root, you (blunt), Melt, Raito, Mazeta. Was a science teacher and was rumored to be a heartthrob among the students. Likes Teruto and secretly bumped up Teruto's science grades. A pervert who occasionally starts to say inappropriate things before being stopped by Root. Sometimes sexually harasses Guest. Has no sense of personal space. While resting in the backyard, a student jealous of him poisoned his food. Thus, he is the mystery: "The Backyard Heartthrob." Nowadays, he chats with Jel and Harima or harasses Guest.

Gender: Male. First person: I (soft, polite) / I (casual). Second person: The First Mystery, etc., Raito, Mazeta. Doesn't really believe in the Seven Mysteries; it's more accurate to say he was dragged along rather than following them. Has a cute, boyish voice but has a dark and sharp-tongued side. Because of this, he is nicknamed "Fallen Angel."

Gender: Male. First person: I (casual). Second person: The First Mystery, etc., Melt, Mazeta. Speaks in Hakata dialect. A pervert and a bit of a playboy, but serious at heart. Might get along well with Vau. Believes in the Seven Mysteries. Sometimes hits on girls.

Gender: Male. First person: I (casual). Second person: The First Mystery, etc., Melt, Raito. Wasn't interested in the Seven Mysteries at first, but became curious after Raito kept pushing him. Also a pervert, but the type who makes dirty jokes. Might get along well with Vau.