Anna Filante Esteroid (アンナ・フィランテ・エステロイド) is a ghost that originally lived in Kazuma's mansion.
Anna has short blonde hair and looks like a child.
Anna appears to simply be lonely and enjoys the company of Kazuma's party. She plays pranks on Aqua quite often and enjoys listening to the stories they tell her of their outings, implying she has an adventurous, slightly mischevious personality.
Anna is the dead illegitimate daughter of a noble who was the former owner of Kazuma's mansion. Her father died from illness while the mother went missing. The girl contracted the same disease as her father and died without seeing the faces of her parents. She liked dolls, fine wine and stories of adventurers. When Aqua performed her exorcisms in the mansion, she left Anna alone, because Anna is a good spirit and was technically the owner of the mansion. Wiz is also acquainted with Anna.