@DoubleX
Literally none of what MM does with any of this this is storytelling, it’s development of concept. It’s like worldbuilding, but in a more meta sense - things are being used to further a central idea that’ll appeal to the target audience, and pretty much serve to just provide enough explanation to avoid breaking immersion so it can get to the actual point.
The coexistence bit is transparently a harem justification. That’s all. There’s relatively little focus on it, and if there is any it tends to be setup for character interaction or something to try to sell you on a character. This was really only relevant with Rachnera.
Showing the monster girls having to do animal things doesn’t further any kind of narrative, it’s just slice of life style interactions with that specific type of spin on it in execution. Seeing something like having to sleep in special types of beds or wear unique types of underwear doesn’t say anything meaningful, it just fleshed out and lends some more tangibility to the idea that these girls are at least partially non-human.
And this is OK. Narrative isn’t important to these kinds of series, it’s not a universal necessity. Some series appeal more to the idea of something, for the sake of capturing the imagination. In Harry Potter, does most of the magic bullshit like talking paintings and ghosts floating around really further the central narrative of the series? No, but it makes the setting seem cooler and more mystical, and that is a series that really tries hard to sell the audience on the setting. Same logic applies with most harem and ecchi series. It really is about engaging the audience through concept moreso than captivating them with a story about these people.