Hailing from the deteriorating creature world, Deckie descended to Earth within a comet swarm to seek a Duel Master who could counter rogue spirit incursions into the human realm. This entity directly encountered Joe Kirifuda, forging a pact to serve as his companion and guide.

Physically manifesting as an animated deck box with a distinct face, Deckie features a white-and-black color scheme and a red bowtie. Arms and legs appear only when situationally necessary. After Joe designated an unknown civilization as "Jokers," a green 'J' mark manifested on Deckie's form, symbolizing this affiliation.

Deckie possesses an energetic personality and encyclopedic knowledge of Duel Masters, often masquerading as an ordinary deck box to evade human notice. However, it exhibits volatile tendencies, deliberately endangering Joe by forcing "True Duels" against Duel Warriors—high-stakes encounters with physical consequences. Initially advocating lethal outcomes for defeated spirits, Deckie shifted tactics after Joe insisted on returning spirits to their native realm. It frequently withholds critical information, potentially due to a belief that True Duel Masters must overcome extreme challenges beyond their comfort zones, influenced by past crisis-era duelists. Differing moral frameworks from its creature world origins and concerns over lingering spirits also shaped these actions. Exposure to Joe's ethics later led Deckie to condemn duelists who kill spirits under false pretenses of justice.

Core abilities revolve around card manipulation and interdimensional travel. Card generation ties directly to the creature world's condition, restricted from creating dragon-based cards due to their extinction there. Feeding drawings into Deckie's mouth typically yields Joker creature cards, though these often behave unpredictably or demand compensation from Joe. Ingesting cards returns spirits to the creature world, while Deckie can analyze a creature's origins—natural or artificial—through its dimensional connection. Inserting photographs grants limited access to past duelists' memories, and forcing a person's legs into Deckie's mouth enables joint travel to the creature world.

Throughout events, Deckie's role evolved: initially tutoring Joe in dueling mechanics and crafting his deck from sketches, it identified the resulting entities as the unprecedented Joker civilization. As rogue spirit incursions escalated, Deckie collaborated with Joe to contain threats like Shizenseijin and Kiradon via Duel Tower encounters.

Exploring the creature world unlocked new powers. Resolving the Fire Civilization conflict by aiding Bad Brand against Kira's Ov Sidia earned Deckie the Mark of Fire, enabling Joe to create Fire Civilization Jokers. Subsequent journeys brought further enhancements: defeating Kabu Toki in the Nature Civilization unlocked Nature Joker creation, while interacting with Cap, master of the Water Civilization, allowed generating Gacharange Creatures to upgrade entities like Johnny and Joragon. Later assistance to Cap during instability caused by Zero and Gap facilitated Water Joker creation through Cap's A.I. companion.

Deckie displayed historical awareness by recognizing creatures and dragons from Joe's review of Kirifuda family archives. Using photos during this investigation unexpectedly transported Joe into a memory-constructed world featuring younger versions of Katta and Shobu Kirifuda, fostering familial connection. Confronting mounting threats to the creature world's stability, Deckie continued supporting Joe with expanding arsenals of Joker cards and Gacharange Creatures.