Sebastian serves as a sentient massage chair drone, fulfilling dual roles as Nail Saionji’s loyal butler and symbolic throne. His humanoid-mechanical design blends massage chair elements, including a hexagonal light-green faceplate and extendable limbs tailored for utility. Integrated into the Garden of Providence—an organization aligned with his master—he prioritizes unwavering loyalty and efficient service.

His combat style revolves around a specialized Chair Deck, utilizing DARK-attribute monsters, spells, and traps themed on thrones and seating. Core cards like *Dahut Ahez the Mirror King of Ys’ Throne*, *Dwell Chair Massage*, and *Collapse Chair* synergize to execute strategies focused on deck milling and tactical resource control, mirroring his thematic ties to authority and subjugation.

Sebastian engages in multiple duels against figures such as Yuga Ohdo, Finger Chikako, and Nail Saionji, consistently facing defeat while reinforcing his role as a recurring obstacle. His customized Duel Disk, distinct from conventional models, complements his robotic design, merging aesthetic cohesion with functional purpose.

Details about Sebastian remain confined to his primary series appearances, with no supplementary media expanding his narrative scope. His documented traits emphasize service-oriented programming, strategic deck composition, and his brief yet persistent presence as an antagonistic force.