[Tyabann]

Spoiler:

I’ll describe in details later, but the existence of that Amaterasu was within the body of Onii-chan, of all people. Or should I say absorbed. It could be thought as "Onii-chan = the supreme deity Amaterasu". To give an example easier to understand for some, it’s "Onii-chan = Suzumiya Haruhi".

That's, uh... pretty blatant there.