Board Thread:Legitimate Canon Questions/@comment-188.247.78.184-20150130015124/@comment-4091815-20150130031248

I don't understand the question really.

The Oni were summoned by Noshiko Yukimura to search for the Nogitsune.

The Nogitsune possessed Stiles and then was able to steal one of Noshiko's tails and take control of the remaining Oni.

The power of the Nemeton was part of the process of summoning Oni but just how that worked we don't know.