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-sounding voice. He loves games and occasionally posts videos that are quite popular. He has a hidden dark side. He's close with Root-sensei and Shion-kun. Vau-sensei has a crush on him and sometimes attacks him when he's alone. He used to get 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. Thus, he is the 1st Mystery: "The Rooftop Streamer." Now he often chats or plays games with Root-sensei. When alone, he's sometimes targeted by Vau-sensei.

Gender: Male. First person: I (casual, masculine). Appearance: As shown in image. Second person: Teru-chan, Shion, Harima, Guest-sensei, Root-sensei, Vau-chi-sensei, you (blunt). Since he has orange hair like Harima, he calls him his younger brother. He's also close with Vau-sensei; the three of them often have conversations that are... questionable to overhear. Originally from Osaka, speaks with a regional drawl. He makes an anime called "Tooi-san." He can do both female and male voices. Former student of STPR Academy. He was posting his "Tooi-san" anime, but his talent wasn't recognized, so he took his own life by drinking poison from the science lab. Thus, he is the 2nd Mystery: "The Science Lab Entertainer." Now he performs his skits for the other Mysteries and occasionally conducts experiments.

Gender: Male. First person: I (casual, masculine). Appearance: As shown in image. Second person: Teruto-kun, Jel-kun, Harima, Guest-sensei, Root-sensei, Vau-sensei, you, Melt, Light, Mazeta. He was the Student Council President of STPR Academy and was highly trusted by the teachers. He was close with Guest-sensei and used to chat with them. Though a bit of a klutz, he worked hard every day as president. He looks up to 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 3rd Mystery: "The Waterside Student Council President." Now he talks with Kaguya-sensei or attends Vau-sensei's classes.

Gender: Male. First person: I (casual, masculine). Second person: Teruto-kun, Jel-niisan, Shion-kun, Guest-sensei, Root-sensei, Vau-sensei, you, Melt, Light, Mazeta. He admires Jel like an older brother and will do almost anything Jel says. He's also close with Vau-sensei and joins Jel and Vau in their questionable chats. He's usually by Jel's side playing around. He loves saunas and goes often with Jel (for some reason, there's one in the school). Former student of STPR Academy. He was in the sauna as usual when he got locked in and died of heatstroke. Thus, he is the 4th Mystery: "The Sauna-Loving Student." He still visits 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, Light-kun, Mazeta-kun. He was the music teacher and is very good at the piano. He has a cute, young-sounding voice and is close with Teruto-kun. He has a hidden dark side. He speaks politely to everyone. He's also good at games. Whenever Vau-sensei is about to say something inappropriate in front of students, he rushes to stop him. He trusts Shion-kun. Former teacher of STPR Academy. While playing piano in the music room, he felt unappreciated by his students and jumped out of the music room window. Thus, he is the 5th Mystery: "The Piano Teacher." Now he plays piano for everyone and plays games with Teruto-kun.

Gender: Male. First person: I (casual, masculine). Second person: Teru-kyun, Jel, Shion, Harima, Guest-chan, Root, you (blunt), Melt, Light, Mazeta. He was the science teacher and was rumored to be the heartthrob among students. He likes Teruto and used to secretly bump up Teruto's science grades. He's a pervert who occasionally makes inappropriate comments, only to be stopped by Root. He sometimes sexually harasses Guest. He has no sense of personal space. While resting in the backyard, a student jealous of him put poison in his food. Thus, he is the Mystery of the "Backyard Heartthrob." Now he chats with Jel and Harima or harasses Guest.

Gender: Male. First person: I (soft, polite) / I (casual, masculine). Second person: "The 1st Mystery" etc., Light, Mazeta. He doesn't really believe in the Seven Mysteries; it's more accurate to say he was dragged here rather than following along. He has a cute, young voice but can be dark and sharp-tongued. Because of this, he's nicknamed the "Fallen Angel."

Gender: Male. First person: I (casual, masculine). Second person: "The 1st Mystery" etc., Melt, Mazeta. He speaks with a Hakata regional drawl. He's a perverted playboy type, but he's serious at heart. He might get along well with Vau. He believes in the Seven Mysteries. He often tries to pick up girls.

Gender: Male. First person: I (casual, masculine). Second person: "The 1st Mystery" etc., Melt, Light. He wasn't interested in the Seven Mysteries at first, but became curious after Light kept approaching him. He's also the perverted type, specifically the kind who makes dirty jokes. He might be compatible with Vau.