I got curious and read the source webnovel to find out more about the worldbuilding.
This is actually an otome game world. MC will remain blissfully unaware this is a game world, he thinks it's just a fantasy world.
The game's overall plot is about preventing the demon king from conquering the otome game's country.
This is done by collecting all saintess regalia (ex. the saintess tiara) and maxing your relationship with either game capture target.
If both are successfully carried out, the demon king will be banished and the country is saved.
If either one fails, the country is conquered and the humans are enslaved.
The game also has a harem mode where you can romance all capture targets and the demon king at once.
There are 2 more reincarnators who know this is a game world, because they played the game. They are both girls.
MC is not close to them to properly find out more.
The current plot ties in with the original otome game's capture target storyline. (MC is reincarnated as one of the targets, but he doesn't know this. ) The tiara's theft would've spurred the original Theo to take up actual divination and become a geniune expert by the time he was a teenager. His plotline would've been about tracking down the conwoman and recovering the tiara. Of course, MC has unknowingly destroyed this entire storyline by calling out the scammer's bluff.