FFXIV X Fate/Extella
Between one breath and the next, Simionn Roseenberg and his half-sister Rachel Lorito find themselves in a strange realm all to similar to the one that Omega had constructed in order to test the two Warriors of Light, and left with no other option but to walk ever forward, they decide to deliberate on the paths that they might take.
Of course, the moment the two choose a direction to start walking in is the moment they're accosted by a strange blonde haired woman in an even stranger dress, demanding that they join her army because "Umu, the two of you seem quite strong!"
Seeing no other path forward, and having no real reason to refuse, the two accept the blonde haired woman's offer, who then proceeds to introduces herself as Nero Claudius, and begin to follow her back to her base of operations, unaware of the trouble they'd soon be involved in.