Well this got weird pretty quick. Still, Kyoukai is by far one of my favorite female leads in all of manga. I'll be pretty bummed out if anything happens to her.
He's not a coward for not killing his main character. Still a business, the story can't go without the main character.
Even though historically, the real man Shin was based on died right here.
It's that he's using this stupid-ass life-sharing deal. The ENTIRE POINT of Houken was to find a way to cause the physical to become supernatural. And yet somehow Kyoukai has supernatural magical arts already. Had them for a thousand years!