Add is a mysterious, sentient black key-like familiar in Lord El-Melloi II Sei no Jikenbo. He serves as a talking companion and tool associated with Gray, often acting as an observer and commentator on events around Lord El-Melloi II. Though small and seemingly simple, Add is knowledgeable, sharp-tongued, and capable of revealing important information or assisting in supernatural investigations. He plays the role of a quirky support character whose presence adds humor, mystery, and practical help to the series.