Delmo is a small, magical bunnygirl with blue hair and blue eyes, always clad in a distinctive costume featuring bunny ears, a tail, tights, a belt, and a bow. Her magic specializes exclusively in costume transformations: she instantly conjures cosplay outfits and physically alters bodies to ensure perfect fits, including temporary breast enlargement. Each magical service requires compensation, typically sweets or food, establishing a transactional dynamic.

She possesses a notably voracious appetite, frequently consuming large quantities that visibly distend her belly—a trait others leverage during negotiations. While her origins remain unspecified, she resides with Chako Hasegawa’s family alongside Sachiko Arii, supporting the East Oizumi Academy’s cosplay club.

Delmo collaborates with Ikebukuro, a small, non-verbal owl-like creature who assists with sewing, ironing, and costume preparation. They communicate seamlessly despite his silence, and he often judges cosplay competitions. Her primary club relationship is with Chako, whom she repeatedly aids by replacing costumes damaged by Chako’s clumsiness. Their partnership includes minor disagreements, particularly over Chako’s dissatisfaction with her physique.

Her narrative role consistently revolves around enabling costume changes and comedic scenarios through her magic. An unresolved subplot involving a mysterious blue-haired woman exists within the series, but Delmo remains unconnected to it.