The Fey Hound Game Over is an ending which occurs if the party loses to any enemy in the Fey Mansion except for the boss Princess Anathema IV herself.
Having never made it to the end of the Fey Mansion, the Cutie Knights never even managed to meet who was responsible for all of this in order to help Vini. In fact, let alone saving Vini, they were unable to even save themselves.
Finally waking up, Eric(a) finds themself with a collar around their neck, with Fairies shouting for them to get down on all fours instead of walking like a person, electric shocks being applied as necessary to force compliance. Not content with only this, they then force Eric(a) to endure torment and humiliation as the fey work to mold her into their dog. Usually made to act like a dog, sometimes actually turned into a dog, Eric(a)'s body, mind, and memories are twisted between canine and human as their fey masters shape her into an obedient hound.
Eventually they succeed, Eric(a) becoming something less than human yet still more than a simple beast: the perfect hound for the fey and their wild hunts. Although the rest of the Cutie Knights are not seen, it can be expected that they underwent similar processes.
A scene is shown an indeterminable amount of time later, Eric(a) already warped beyond recognition as a fey hound, tracking down some unfortunate victims. Alongside her in her hunt is the fey-turned Vini who succumbed to her transformation without the Cutie Knights managing to save her. Competitively, Eric(a) is determined to beat Vini in this chase so that she can rape the subjects of their pursuit, and one specific man in the group in particular. In this form, Eric(a) has become a lust-crazed monster girl so twisted that even the warped Vini finds her crazy.