That's what happens when he's too horknee for Ariel. He's thinking with his second head below (=・ω・=)
I am partially unsurprised after thinking that the Emperor is like this toward Arielle when he was pretty much the exact same towards the original Elvia. He spoiled the OG!Villainess to pieces and overlooked her MASSIVE misdeeds and shitty rep. Yet actually wants her to be upstanding and praised her when our FL possessed her and turned her around, completely overlooking his part in raising her to be so rotten.
But while it’s good for him that Elvia is now capable and independent, I feel like he likes the feeling of taking care of someone, even if he is so BAD at it, so Arielle fits him very well now that Elvia no longer really needs him. He’s also a massive people-pleasing sucker when it comes to his family and Arielle is louder with her tantrums than Elvia is.
Maybe the Emperor has a hero complex, which is why his affection rose so quickly when Arielle faked a faint just one time. Maybe he just has a ruling complex from being emperor. Maybe he’s just horny, like other people have said, but now that Arielle is ‘family’, he has to spoil her as a little sister instead. Maybe he has a weird complex on family; I don’t see any other relatives coming into the picture in over 100 chapters; when you’re family is that small, you’d do anything for them. Either way, he is emotionally stupid or naive which is why he keeps trying to force these two women to play happy family and has no spine in calling out bad behaviour.
I genuinely have no idea why the Emperor's affection for Arielle is so high. He's aware of Arielle's rotten nature, yet he always turns a blind eye to her wrongdoings. Why did his affection for her go up so quick?? It's so odd to me, especially seeing how Arielle does not seem to shy away from displaying her detestment towards the FL who has bonded with the King through their whole lives, as compared to Arielle who came in his life just recently.