Seven years have passed since the events in "Stan Helsing". Stan and Nadine are now married, and have four children, two boys and two girls, named Stan Jr., Nadine Jr., George, and Freyja. The couple and their friends have formed a group known as "Stan's Slayers". One day, while Nadine is at the bank, she gets a call on her cell phone from Stan, saying that Stan's Slayers are needed in Japan urgently. And so, they head there, and are told that Japan is under siege by giant monsters: Nagoya is under attack by a giant scorpion monster known as "The Red Scorpion", Tokai is under attack by a giant blob monster known as "The Slop", Yokahama is under attack by a giant alien monster known as "Gearlala", Osaka is under attack by a giant gorilla monster named "Emperor Omperor", Fukuoka is under attack by a giant bird monster known as "The Giant Beak", and Tokyo is under attack by a giant dragon monster known as "Goodnesszilla". Knowing that the group can't handle the monsters on their own with what they already have, the JSDF had already built them four giant robots to combat the monsters. The group is then taken to each of their respective robots, which they then take control of, and head out to fight the monsters. After five of the monsters are defeated, all four of the Stan's Slayers meet in tokyo to battle Goodnesszilla. He proves to be harder to beat than any of the other monsters, but eventually, they manage to do it. After reporting back to the base with the captured monsters, they prepare themselves to leave, when Teddy inadvertantly releases them again. All six of the monsters then attack and savagely destroy the robots. When all hope seems lost, a giant flying turtle with a clam-shaped head, known as "Clamera", flies in, and fights the monsters. Clamera defeats the monsters, and takes Stan's Slayers home.