Please don't jump me for this, but merize and azael's relationship have a pretty problemat...

The power of love I guess

there was no way of telling their story without it being somewhat problematic. She is trapped in another world where her kind are eaten. Any relationship with the race that eats her kind can be viewed as problematic regardless of how slow it progresses

Thats very true, could've been a lot less problematic though. Off the top of my head, she could've been hiding her status as a human like Iruma, and organically fell in love with henri, the worst part in my opinion is the fact she was being confined in an observation facility and had a relationship with her bodyguard.
Iruma as a human also has organic friendships and relationships with other demons despite being a human, the author had a choice in writing henri and merize's relationship however they wanted, the fact that they chose this specifically just leaves a bad taste in my mouth.

can’t deny it’s problematic, but it makes sense considering their situation. merize is trapped in the netherworld with no memory at all, so of course she would come to like the only person who treated her sincerely and even created spells to help her understand the demon language.
and henry is enamored with merize not only because she’s human, but also because she’s adorable. he even deludes himself into loving her enough to suppress his bloodlust through his romanticism.
so is their love healthy? of course not. should the author avoid writing it this way? no. it’s interesting to explore love in all its forms, healthy, unhealthy, or toxic, and demons obviously don't care about morality, look at clara in her wicked phase

Yeah I agree, in the end this is only a small part of the manga, I honestly doubt production cared enough to put that much effort into a side characters backstory. I'm pretty sure the editing team just threw ideas at the wall until something stuck, so unfortunately I doubt they're gonna explore any of the toxic connotations behind a relationship like this, which is a shame could that would be interesting to see.
I mean they did talk about it a little when one of the guys (I don't remember who) was like oh you only like her cause she's a tasty weak human, but they didn't really address it, henri just steamrolled through.

+I in no way think it's wrong for then to have fallen in love because like you said it's only natural, their love story being bad was never my point, I just hope they manage to wrap up this important story arc without it leaving a bad taste in my mouth.