Yeah, it seemed Yuto's hatred caused him to go temporarily insane, but thankfully his friends restrained him long enough for his adrenaline rush to wear off which allowed him to calm down on his own. It was interesting how he didn't become self-aware of Yuto's soul inside of him until Mieru pointed it out. He also figured out that Yuto's anger, when fused with his own, makes him go berserk, but he's not consciously aware of his actions when in that mode of rage. I'm guessing that when his Berserk Mode "turns off" he suffers from some type of short-term amnesia. Huh...kind of reminds me of Yugi and Atem in the original when they first fused together.
On the bright side, at least we got some epicness out of it!
I'm sure those Obelisk Force guys saw their lives flash when Yuya summoned Odd Eyes Rebellion/Supreme King! I was grinning from ear to ear when I saw it and actually paused the video to take a good look at that huge dragon!