Pandora, Pandora, a stunning young woman, and her son flee a prince who is secretly in love with her. The prince, furious to discover she already has a child, aims to hand them over to the God of Nothingness, a colossal slimy monster. When all hope seems lost, a skeleton pirate arrives on the scene—the Captain of the Dead—driven by Pandora’s promise to sacrifice herself to save her child. On board his ship, a mermaid figurehead named Sleeping Belle watches over a crew of varied monsters, and Pandora and her son undergo a chilling transformation into immortals who will never age.
Yet the God of Nothingness, enraged at missing his fresh flesh, devours the soldiers. The prince pleads for mercy, and the monster agrees; after swallowing him, the being is transformed into a moon-headed entity baptized as the Gibbous, and he sets out to seek revenge on Pandora and the Captain of the Dead. To keep their little family safe, the Captain flees with Pandora and their son—now known as Little Vampire—across time, hopping through ages where they encounter a motley cast of monsters who will join their ranks: Marguerite, a creature inspired by Frankenstein’s monster; Claude, a radioactive crocodile; Fantomate, a tomato-dog; and Ophtalmo, a wily monster-inventor. They all end up taking shelter in a mansion on a hill, where the Captain creates a dome to render them invisible.
Three hundred years later, Little Vampire grows tired of the film club that gathers the other monsters and their endless debates. He escapes with Fantomate to pursue an education among humans, determined to meet real children. He befriends Michel, an orphan who lives with his grandparents and believes in monsters, after Michel discovers in a mathematics notebook a window into a hidden world. The friendship deepens as Little Vampire helps with Michel’s homework, and Michel longs to meet him in person. He even carries with him a kawai, a human transformed into a bug by the Gibbous, trapped within the notebook.
When Michel is brought into the fold, Little Vampire and his friends attempt to keep him safe from the Gibbous’s reach. They return to Michel’s house, where Michel’s presence complicates their invisible sanctuary. The Gibbous grows possessive and threatens Michel’s grandparents unless Michel reveals the hidden friends. A trap door leads Michel to Little Vampire and the monsters, and the group resolves to confront the Gibbous once more, with Fantomate and the others rallying to protect Michel.
The pursuit culminates on the Captain’s boat, where they confront the Gibbous in a tense showdown. Pandora, the Captain, and their crew race to recover Sleeping Belle, who has been put to sleep by the Gibbous, while the Gibbous imprisons Michel and the monsters in a bag. A brave scramble ensues as Fantomate warns Pandora and the Captain that Little Vampire and the others have been seized. In the ensuing rescue, Little Vampire, transformed into a mouse, frees his friends and the crew engages the Gibbous in a duel, with Pandora stepping in to restore balance.
Facing the Gibbous, Little Vampire reveals that revenge will not heal him, and that companionship matters just as much as power. The Gibbous, moved by this realization, admits he needs company and friendship; the kawaii agree that they like him, too. Little Vampire guides Sleeping Belle to awaken the sleeping princess—an act that breaks the spell and helps the Gibbous regain his humanity. Sleeping Belle frees herself from the ship and takes the Gibbous’s hand, and the two depart together, while the kawais decide to build a small, hopeful democracy in their world.
With the danger passed, the dawn reveals a calmer future. The Gibbous is no longer consumed by vengeance; Pandora recognizes that love gained through shared moments can outshine raw appetite, and the Captain’s crew can finally move about their mansion without fear. The next day, Michel shares with his class how he and his new friends pulled off their daring ruse, while he and Little Vampire—along with Fantomate, Marguerite, Claude, and Ophtalmo—head to the beach to play under the watchful eyes of Pandora and the Captain of the Dead, who now enjoy a quiet life beyond fear.
