I think that Mitsuzane is in a very difficult situation, and his evil actions mostly stem by the fact he doesn't actually know what to do if he loses control.
In my opinion, Mitsuzane completely changed when he joined Yggdrasyl. When he was part of team Gaim, before being told the truth by his brother, he was happy, and the only lie he did was pretty much hiding his true identity as the son of the Yggdrasyl CEO. Besides, he was on the same side as Kouta and team Gaim, meaning he wanted to know the truth and what Yggdrasyl was hiding. Whiel he showed a ruthless side, especially with someone like Sid, his loyalty with Team Gaim was total.
Once he joined Yggdrasyl, and I feel he did it because he genuinely felt the firm was trying to do the best it could under the circumstances, he ended in a much more uncomfortable situation. Not only he was often at odds with Kouta, who, instead of being his ally, became his opponent (even if Kouta don't know that), but he had also to hide to others the truth about the Hellheim forest (his stunt with the Lock Seeds in episode 26 was following that trend of hiding the truth, as his brother wished (and not without reason)). As a result, he knew that the only way he would be able to stay with his friends, since it's the only thing that has ever made him feel happy, was to lie even more. The fact that the Beat Riders were at odds with Yggdrasyl (especially Mai) was hard for him, since he's part of the firm. As a result, he ended up being a double agent, and it's obvious that as a double agent, he's forced to lie all the time, and especially, being in control of everything.
It's obvious he suffers from that ; I don't think he has pleasure being such a control freak, and he felt an intense pressure.
He was especially frustrated by Kouta's actions because it meant he was forced to become his enemy, while he didn't want to: he hoped Kouta would trust him, but instead, he ignored him and kept fighting against Yggdrasyl, ans, as such, against him. He at least hoped to keep Mai and his Team Gaim pals outside the fight, and the Hellheim business, because he alsi knew that it was the only way for him to be both loyal to Yggdrasyl and stay with them.
At the end, he completely failed, and in episode 26, he was forced to hurt Mai and his Team Gaim pals, out of loyalty for Yggdrasyl. He was furious about it, and blamed Kouta for that. But once Mai slapped him, he felt that he was rejected by the one he cared the most. As a result, he became pretty insane, and because he doesn't know how to deal with the situation, he ended up blaming Kouta even more, and he ended up trying to kill him. It doesn't excuse what he did, but I feel all the pressure he had within himslef was so big, that it ended up destroying his sanity, because he doesn't even seem to realize that killing Kouta won't solve anything.
The tragedy about Mitsuzane is that when you look at his situation he has no real friend. Even if Team Gaim was friendly to him, he had to hide them the truth about who he is, and he can't share his burden with them. Likewise, in order to be with the people he felt happy with, he had to lie to his brother. And it's obvious he doesn't trust Ryouma and his goons. Noone really knows Mitsuzane. As a result, he never had someone to share the pressure he felt with, because he couldn't tell the people he know the full truth. He chose to endure the pressure, but it ended up being too hard for him, and he ended up losing it.
Micchy needs to be slapped and beaten up, but he also needs help, and a lot of it.