For now, the only method for the brainwashing is to use Shield Prison to seal them off; nothing else would work.
But, the problem is that the scale is too big.
I would have to take into account the magic consumption and the cool-down, as well as finding the ones that Itsuki was controlling.
Just like Ren, he could be corrupted by a curse, but someone must have given him the idea.
But, manipulating him would be difficult.
It could be similar to Ren, where he keeps on repeating what he believed in.
Just what kind of person is Itsuki?
He has an usually strong sense of justice, yet he is also conceited.
How would one manipulate such a guy?