Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-24458290-20140219150427/@comment-42.61.226.96-20140220134751

Well, there seems to be hints towards the Japanese-American camp during WWII.

Also, it seemed to appear after the nemeton was powered up.

Furthermore, it seems to recognise Kira's mom, which means it had a history with her, and we all know how long a lifespan a supernatural creature has.

Therefore, my theory goes like this.

During the Japanese-American camp during WWII, the Nogitsune was probably a resident or possessing someone in there and playing pranks. However, it most likely got treated badly (its a prisoner of war camp), and thus was offended. So, it went on a rampage. However, Kira's mom sealed Nogitsune into the nemeton to put and end to it. So when the Nemeton got powered up, the Nogitsune woke up and broke free, thereby possessing Stiles. He then want to get rid of the entire town (because it used to be a place where he got treated badly).