My theory, based on what MC said about Celestine (?) the OG FL, is that she's a fake and perhaps MC is the real one but her powers have been sealed somehow, causing the illness she has. She mentioned how it was weird how the Duke and the prince, despite being close friends, suddenly became enemies after meeting OG FL... she mentioned how it was quite sudden. Makes me think Celestine (?) can either brainwash people or manipulate them somehow...
This would also connect as to why the temple was behind the assessination attempt and the 'saint' was the one to save him... she can probably use her power as both good and evil (since MC is also warned that divine power can go both ways).
I agree... Besides, from that flashback of Kadien/Kaiden(the ml), it seemed as if the priests from the ancient temple were using their divine powers to turn the little Kaiden into a "puppet in house Mercedes" for them.... Maybe, the og fl saintess Celestine has perfected those powers.... Maybe she has already got the emperor under her thumb....
Also, I'm assuming she's the reason that professor Cuspert had a sudden passion in Igrid..... The silhouette of "her" mentioned in his diary seems awfully similar to the saintess'.....
Hrmmm let me guess.... she's the real saint and there's a fake saint there from the sorta other god worshipper