Due to a burnout with Takanashi Hoshino's actions, and hearing her plea for help after his involvement with killing the Basement Dweller, a forgotten member of Gematria, Sensei, or his real name of Asahi "Kaname" Ikesugi, a 16-year-old student with the unexpected maturity of an adult, is suddenly given visions of a time that never was... or rather, what WAS going to happen. In the vision lies two Sensei, the one who gave everything to Kivotos is now running for so long in 5-6 months, and the other is a usurper that Asahi calls the "False Sensei", a charming but hollow man whose immaturity of a child, openness of Teacher-Student Relationships, and lack of skill and talent in leadership had made the other Sensei run because he charmed nearly every student in Kivotos, and those who aren't swayed are either suppressed or can't act out of fear, or they chose to do nothing about it!
The dream wasn't anything good before the False Sensei eventually died, after a week from his 6 months of planning, due to a poorly executed plan to assault the Black Market District, and he was ended by a grunt from Kaiser Corporation to convey that he was NOTHING without the other Sensei doing the work; he was a wish-fulfillment of insanity, a fanon version made manifest that had no backbone when facing reality. But despite his tears, he knows that this vision could come to pass if he does nothing, so Asahi decided to spin the vision as a story to convey the warning, not knowing that other Sensei, and the students related to the vision in Kivotos, are experiencing the same thing. This means that while he doesn't know yet, he and the other Sensei (yes, there's MORE than one Sensei), including the students in that vision, are experiencing the dream and their actions will decide where the timeline they live in, will go.
[This is a fanmade event idea modeled after Akusaka's "Repent" on AO3, and it takes place after "Volume 1, Chapter 3", and before "Volume EX: Decagrammaton, Chapter 2"]