I was just thinking whether it is possible for ordinary sharingan genjutsus to control the bijus because obito supposedly just used some genjutsu with his sharingan and controlled the kyubi. According to me, we haven't seen any other jutsu apart from kotoamatsukami that can control any other person. So, does that mean obito used ka on kyubi. But that should be impossible as shisui's both eyes were already acquired by some other shinobis.
So, what do you think, what was the jutsu with which obito controlled kyubi.