The Sissy Maid Game Over is an ending which occurs if Eric(a)'s gender is revealed by Olivia. This can either happen by failing to drink the potion made by Wendy, going to Olivia without the potion made in the first place, or not getting enough affection from Marianne. Note that evading this when drinking with Marianne requires getting her trust high enough, otherwise the player is still sent to Olivia's office and thus the Bad End happens.
During the ending, Olivia puts a painful maid headband on Eric(a), who passes out, and recovers to see their body has been feminized, though they have kept their dick (now notably shrunk and permanently limp). Olivia then sells Eric(a) as a sissy maid to one of Marianne's associates, a strange and sadistic man with "peculiar" preferences, the headband twisting their mind so they come to love their work no matter how awful it becomes.