Joma serves as one of the film's two primary antagonists, a fraternal twin doll alongside Makao. Together, they wield dark magic to dominate Henderland through manipulation and enchantment. Their schemes include orchestrating the capture of Prince Gorman and Princess Mimori, imprisoning their souls within a snowman and a doll to solidify control over the realm. They command subordinate creatures—Cre.G.Mad, Chokirin, and Snowman—to enforce their authority across the park.

Operating from a Henderland palace, Joma and Makao lure visitors with forged invitations, replacing them with enchanted puppets to preserve secrecy. A stolen suit of magical cards, taken by Toppema, becomes their critical vulnerability, prompting a relentless pursuit to reclaim it. When confronted by the Nohara family, they suffer defeat in both a dance competition and a card game, exposing their weakness to the Joker card’s magic.

Shinnosuke triggers their destruction by placing the Joker card atop their castle, causing its collapse and obliterating Joma and Makao. Their demise shatters all curses, liberating Prince Gorman and Princess Mimori. The film does not detail their background or origins within Henderland, and they appear in no other seasons, films, OVAs, or spin-offs.