I have a theory. I don't know if someone already shared this but:
1. The Pope has the ability to Rewrite coz he's an otherworlder as well that probably fell in love with an Elf Girl and then came Annette which is his daughter.
If he had that kind of ability to rewrite everything that is happening in their world, he can easily declare himself as someone holy to the eyes for everyone. Something must have happened before that separated him to Annette or some sort of backstory.
2. The portrait/picture that Sensei found in the library was not Annette but actually her mother. Notice the eyes were different to the drawing of Annette? I feel like it was her mom's portrait.
3. To support my claim in No.1, notice how the pope as well does not have any elf ears or some sort? I don't know if it's just hiding underneath those clothes of headpiece but for me he's human.
If my theory is correct, Sensei is a huge threat to him in a way that he can take away Annette (unintentionally or intentionally) while he might be sent back to his world.
And just a side opinion for those who are complaining about Sacchan & Sensei not being together anymore, guys this is a work of fiction. It's the author's liberty whether they want the character to stick to how the person in real life was or not. It doesn't make the story bad in a way that he's still suicidal but he's just not ready to die yet as he still has some stories to write from the other world. And it was a desperate move from Sacchan especially now that she is working togethrr with the pope just to get him. You can take what you want but not to the point of harming others.
That is all so excited for this arc to unfold! Hope everyone respects my opinion and theory.