How do I introduce the idea of Zevism to my mother?
If you can do magick tricks as proof, then you have a much better chance. If you can spin a psi-wheel or make a cloud rain in front of her, then just ask her to cast the demon out of you in the name of her god. When nothing happens, and you are still able to perform "supernatural" actions, it will be a very strong case against her religion.
That would be unwise, as it takes quite a bit of spiritual power and energy to make "displays" of magick, which would be dismissed as pure "evil" witchcraft by a christard, and if Sero was that advanced, he could simply begin speaking to his mother's light body and begin influencing her dreams and subconscious thoughts.

