mission concept: while trying to repel some of an alien invasion force, the aliens came at them in too strong of numbers with too big weapons, and the future fleet had no choice but to wipe out the entire alien invasion force in self-defense.
the problem was, that fleet in the other timeline was going to do an attack on Earth that would shape the life of the First Galactic Emperor of Mankind
but they have to stop all the super robot alien villains trying to destroy earth
meaning that, in order to protect their own timeline, the future fleet has to do that attack themselves.
but not, like, a mecha pilot or anything.
the first Galactic emperor from the future timeline
resurrected by DG cells
empowered by getter rays
imbued with the G-Stone