I don't know why so many people are arguing for twists. That's literally what M. Night Shyamalan got bagged on for, and rightfully so. Twists for the sake of twists is garbage.
You should be arguing for well written plot developments, not shocking twists. The journey is what you should be rooting for, not sudden shocking changes.
That being said, I don't think this is the body of Edelweiss, based purely on the bottom panel from page 3, Calmia isn't as buxom as Edelweiss is. I think it's more a function of her voice sounding similar to her. I am sure Takeru would instantly spot it, if it was just Edelweiss with Horns. In the introduction scene, it was more like that's the scene he was expecting to happen again. And he was shocked that it wasn't her welcoming him back. Betrayed by nostalgia. And if Calmia wanted to really mess with his mind, she would have appeared as Edelweiss with whatever illusion magic she was originally using, if that was the case, and then done a reveal about it.
Regarding the Prime Minister, it's sounding more and more like he was a member of a death cult. There was actually shockingly little in the story about what the religions and pantheon of this world is like. So we don't know anything about what the gods are like/do they actually exist. The PM could just be a fervent believer of something, and not necessarily a puppet puppet. Like stories of demon worshipers who invite a demon into themselves. And it might not be Angels in the traditional sense either. It's not like he went SSJ, he just raged out. One would assume being taken over by a powerful being would increase his base stats, but he just gets mad.
Edit: Oh, and I forgot to mention, I'm really glad the people at the execution aren't the same civilians running from the massacre (aside from the military and the executioner). I read back specifically to see if I could spot any of the same people. You don't want/need to make them all the exact same people to emphasize the tragedy of the situation. Making them all hypocrites really dulls the reader into accepting violence.