the mmz nine sols au! im still working out the broad details but the idea is that x, zero, ciel, dr weil, and the four guardians are all sols working on curing the tiandao/maverick virus, and X actually is able to create a cure for it! but dr weil, wanting to use the virus to control the solarian population, kills x and zero and creates genetic copies of them (copy x and omega) so he can continue his scheming unimpeded. X is dead for real but zero survives through some means similar to yi and is eventually awoken by ciel who has grown suspicious of the council's motivations and wants his help taking them down.