Student ID

Every student in the Advanced Nurturing High School is given a Student ID and number at the time of admission. This number was believed to be unique until Kiyotaka Ayanokōji noticed Mio Ibuki and Masumi Kamuroto having matching ID number in Light Novel Volume 9.

Unknown Pairs
Leaving the following two students: The rest of student ID matchings are still unknown.
 * Mio Ibuki and Masumi Kamuro

Trivia

 * Arisu Sakayanagi seemed to also know about the students having matching Id's. It is shown in Light Novel Volume 10 when she asked Tomonari Mashima(Class A homeroom teacher) whether Kōhei Katsuragi will also be expelled, following Haruki Yamauchi's expulsion Mashima replied, that doesn't work like that. Here That means the matching student ID.


 * Even the Student Council President, Manabu Horikita never knew about this. He deems that this is something the school had just devised. According to him, this is something that might be helpful in the future.