The Beach Babes Game Over is an ending which occurs if the party loses to the Nereid during the Return to Mermaid Caves.
Upon losing to the Nereid, Eric(a) wakes up to the spirit trying to give Veronica breasts, the recipient violently objecting moments before having her brain shut down and made into a flatty bimbo. Alice can barely persuade before having a dick-shaped gag shoved into her mouth and made to practice sucking on it frantically. Eric(a) then realizes they cannot control their body due to a paralyzing poison, and Nereid reveals she will "reeducate" them as the sluttiest bimbos to ever walk on land. Eric(a) can't get a word in before Nereid puts them under her charm.
Several years passed, and everything that happened in the caves is but a hazy memory to Eric(a). In the end, Nereid kept true to her promise, sending the group back on land and restore their human form, albeit with their personalities irrevocably changed: Emmy, Nikki, Allie, and Vivi, all beach blonde bimbo babes with barely any resemblance to the old Cutie Knights sets out to have a competition every day to see who fucks the most boys and girls.
Eventually, however, Nikki slowly recovers possibly due to her nature as a succubus, leaving the other three girls permanently reduced to beach sluts. Even Marianne can do very little to reverse the effects, but on the positive side the four girls have reestablished themselves as the Cutie Knights, with Nikki somewhat enjoying her status as the smartest and most responsible member. But Eric(a), their old identity gone forever, now remains as a horny, happy bimbo named Emmy.