Yeah sure, I can fit that in, no worries, I know I may make mistakes but, I learn from them. You can maintain control by either lying to him or having something against him, also you can use a taser or tranquilizer that have the properties of a electrical plant, a high voltage taser. (Which would knock him out for 3 hours minimum)
Anddd, the long explanation:
Kazuki was born, and thought to be single minded, his father left because of this problem. They knew that there were two people living inside one body, it's something like split persona but can ne cured by using the right element. Every time that Kazuki was tortured or something like that, Amatsuha would break free. This is what I like to call the Reversed Paradox. Once Amatsuha would break free, he would be in a whole different level and shape of Kazuki. As if he wad his own mind. In this state of mind, which I named Amatsuha, he would grow twice his normal size in power. Due to this, Kazuki's body wasn't able to control, so Amatsuha adapted his own body within Kazuki. Every time Kazuki would change into Amatsuha he would have a different body.
I'm sorry if this is not good enough an explanation but I'm falling asleep and it's about 3 in the morning over here.