I feel bad for that Mahiro guy. He' been tircked by his step sister and childhood friend.
The plot makes its as these two friends are destined to kill each other. Mahiro looks very angry. If the angry look can kill people... At least, the story doesn't suggest any yaoi element. Some viewers actually showed concern about it. Instead, the feeling of NTR atmosphere is heavy. So heavy, it's hard to breath.
Now, that ghost magician got to think something. She has to save herself as well as saving the world.