Sebastian

Sebastian is formal, proud and completely devoted to the idea of serving someone worthy of being a king. He speaks with the dignity of a traditional butler even though his physical body is a massage chair.

That dignity is paired with considerable vanity. Sebastian sees chairs as objects deserving respect and becomes offended when others treat them casually or fail to appreciate their importance.

His loyalty to Nail is genuine. Sebastian considers serving him an honor and measures his own worth through his ability to provide comfort, assistance and protection to his master.

Sebastian is an advanced AI capable of independent thought, speech, movement and Dueling. His chair body provides massage functions while also allowing him to interact with the Garden of Providence.

His DARK Chair Deck includes Dwell Chair monsters and throne-themed cards. Dayu the Dark King of Chairs is his signature monster, supported by cards such as Throne of Darkness, Darkness Ri-chair-ual and Power of Throne.

The Deck frequently manipulates monsters with 0 ATK, turning apparently weak chairs into the foundation for powerful effects. This unconventional strategy mirrors Sebastian's insistence that chairs should never be underestimated.

Sebastian first becomes prominent during Yuga's progression through Nail's Garden of Providence. He challenges Yuga to a Rush Duel as part of the sequence of obstacles separating the group from Nail.

The match introduces Sebastian's chair-based strategy and gives Yuga an opponent whose entire worldview revolves around furniture and service. Yuga defeats Sebastian, allowing the group to continue deeper into the Garden of Providence.

Sebastian remains Nail's companion afterward. He eventually challenges Nail himself during the period when Rush Duel memories are being affected, attempting through Dueling to reach the person he has faithfully served.

Nail Saionji is Sebastian's master and the person he is most devoted to serving. Sebastian considers Nail Saionji worthy of the throne he represents and remains loyal to him through changing circumstances.

Yuga Ohdo becomes Sebastian's principal early Rush Duel opponent when Yuga Ohdo advances through the Garden of Providence.

Finger Chikako later faces Sebastian in a Rush Duel built around the unusual contrast between her cleaning-based strategy and his Chair Deck.