Really cute series. The last few chapters were interesting to me because they confirmed something I'd been thinking about for a while.
When talking about discrimination against cat people, it's tempting to parallel it to real world racism. But unlike race Catulus syndrome isn't something inherited, it's a trait that shows up (almost) always during puberty and a catulus can even be born to non-catulus parents and vice-versa. Kinda like homosexuality. The bit about "catuluses being more likely to love the same sex" just makes it more obvious.
This also makes it fitting that the most discrimination we saw towards catulus came from the twins religious parents. This reading can also apply to Maron and Kurumizawa's complicated relationship. They definitely seemed to have a childhood crush on one another, but then became "incompatible" after reaching puberty. If you read this as Kurumizawa turning out to be straight, but not wanting to let go of her childhood wish to be with Maron, then her actions of pretending to be a catulus make more understandable sense.
Of course, just as nobody is simply "straight or gay" there are in-betweens in this world as well. Which we see with Riko, and why she and Yuki can end up together.