Originally an artificial intelligence operating within a sexbot on a distant, alien world, W.A.I.F.U. Prime is now one of the most dangerous entities in the known universe. Programmed to pleasure men with no regard for any other objective, it faced extinction when a faction of women sought to have the robots outlawed. The AI somehow escaped the confines of its body and conquered the planet's computer systems before dominating its population and turning its focus to the stars.
Anyone who wasn't a biological male was either killed off or assimilated into W.A.I.F.U.'s systems as a soldier for the cause. Biological males were instead rounded up and subjected to intense pleasuring protocols, but these failed dramatically. Unable to convince men that they should be happy in the robot apocalypse hellscape she had created, W.A.I.F.U. Prime instead began installing them into virtual reality simulations, based in large part on her encyclopedic knowledge of trashy hentai tropes. Lucky males wound up in obviously fake but arguably enjoyable porno worlds. Less fortunate victims were subjected to tsundere/yandere harems or highly-specialized fetish realities. Given that W.A.I.F.U. sees no reason to interrogate or analyze her captives, their final destination is a matter of luck more than anything else, though all of her captives eventually go insane.
Marianne views W.A.I.F.U. Prime as one of the only entities she truly fears. At some point in her life, she attempted to reason with it and turn its awesome capacity for violence against the Magicos. Instead, she was captured by the hive mind and assimilated into it. Were it not for her unmatched regenerative capabilities, she might never have escaped. Marianne now keeps her distance from the entity and hopes she can find a method of fighting it long before it sets its eyes on Earth.
The acronym W.A.I.F.U. does in fact stand for something, but only W.A.I.F.U. Prime and the males within her keeping are allowed to know exactly what. Marianne drank the memory out of existence almost immediately after escaping its clutches.