Sebastian is a character of the day who appeared in The Treasure Is All Mine!, as James's butler. He did not receive a name in the Japanese version.

Sebastian was shown to have a fondness for James and was also worried about his future. After meeting James unexpectedly in the mansion, he tried to catch him and make him marry Jessebelle, in accordance to James's parents' wishes.

After initially failing, Sebastian contacted Jessebelle prematurely and informed her that James was in the mansion. He assisted her in trying to capture and marry him. Though they were successful, James eventually managed to escape from the mansion, but unintentionally brought Jessebelle with him.