Okay, my theory involves the dreaded tengu, but not the Dark Uchiha bullcrap that we are used to. This tengu theory involves only one tengu, and that is Itachi.
Karasu Tengu ("Crow" Tengu) 烏天狗
The ancient form of the Tengu was the "karasu" or "crow" Tengu. Portrayed as an evil crow-like creature with the body of a man, it was capable of kidnapping adults and children, starting fires, and ripping apart those who willfully damaged the forest, for the Tengu live in trees. Sometimes, too, the Tengu would abduct human beings, only to release them later, but the "lucky" survivor would return home in a state of dementia (called "Tengu Kakushi, meaning "hidden by a Tengu").
The most obvious part is the crow part. Itachi is notorious for using crows. The kidnapping part is represented by the fact that, as a member of Akatsuki, he must "kidnap" adults and possibly children. The starting fires is obviously Amaterasu. He was also protective of the leaf as he ripped apart his clan. Itachi's lucky survivors are Naruto and Sasuke. Sasuke went mad when his brother kicked his ass, and starting being emo about the whole thing. Naruto was in a genjutsu when Itachi gave him some sort of power.