Movie background, ABO settings, multiple AO gender changes.
(Anyway, I wrote ABO just for this kind of immutable gender change)
CP: Wolves, Ice, Fire and Ice, EC. Each pair plays their part naturally, and I'm not sure whether it's the Wolves or the Ice and Fire.
The time is set in 2006 (the beginning of the second part of X-Man) in a future that has been reversed by Logan. Although Logan has no memory of 2023, he is already teaching at the college due to historical changes, but he and Scott are still love rivals ╮(╯_╰)╭.
Twins of ice and fire, but they don't know each other.
All in all, this is a story about Mystique being bored and causing a mess.