[Seitsuki]

I think a plausible sort of explanation is something like this:

Spoiler for spoiler tagged in case:

Kyousuke doesn't want the stigma of a killer (no matter how possibly justified) of being attached to Haru, which is why he tried so hard to paint himself as the villain and throw the police off track. The result however is that he does come off as some heartless manipulative bastard, and taking this into account the judges don't lock him up just because he killed the Maou but because he did it for dubious reasons and is dangerous. Pretty stupid anyway imo but yeah.

On the other hand, I think it's really sweet how there's no way to mess up your relationship with Haru. It's like you can be enough of an asshole to screw over every heroine in the series except one, the one you truly love. Ahhh, how romantic. It's fate I tell you. *dies happy*