@Doctor_Hoot - we just came to call them after their hair styles- hime = princess - the long haired girl has what is called a princess cut. The other girl is being called either bob-chan after her bob cut, or some call her antenna-chan.
I guess for whatever reason the author just doesn't find naming them important.
^/^^ Imo these two's relationship is very subtexty. Mana (the shorter girl) worships Nekomusume (the taller one) and is constantly hugging her. Mana even cosplayed as Nekomusume on halloween.
When I saw an "would you click the button"/"I see this as an absolute win" meme containing this image, I knew that this site had this image, and went out of my way to find it. AND HERE I AM!
Yeah, much more like polyamory than NTR. Haruka is kind soul enough for this. Yuu might be angry(for one day) or may join together, who knows. Totally canon.
@Valanz Not really. Although I'm more into sister-sister (NeptuneNepgear, FirisLiane Yes, I know Liane is adopted...) than "father" and daughter. Although this is fine too.