Board Thread:General Discussion/@comment-180.183.8.182-20150722131359/@comment-1915363-20150723113828

They're basically shikigamis who acts as the (substitute) crews to the actual sailors of the historical ships. They are granted the knowledge to operate every armaments equipable on a Kanmusu, and their presence decides whether the weapon may be operated by a Kanmusu (they're device driver equivalent for Kanmusus).

Also, the fairies are not related to the souls of the sailors thet were once aboard them in any way. Instead, they're crystallization of the memories of "accumulated knowledge" from their historical ship, armament and planes.