There is a novelization of the game called Ico: Castle in the Mist by Japanese author Miyabe Miyuki, written out of appreciation for the game. The novel provides backstory in an alternate perspective for the characters not featured in the game, and Miyuki's personal interpretation of the story. The novel is thus considered to be non-canonical.

Miyuki thanks the games producers and creators in the closing comments for allowing her the creative freedom with the story and the use of the same cover art as the game.