(Yeah, that really happened.)
The answer is Miia, I guess. She seems a little more developed than the others.
Actually, there's a bit of laziness later on, as characterization and naming becomes even more defaulted.
Like, the Arachne's name is Rachnera. They're not trying.
Oh, there are OVAs.
In one, the girls exercise at a gym designed to accommodate all species. Shenanigans ensue.
In the other, the daughter from Rachnera's original host family comes to take her back. The girls put her to the test. Shenanigans ensue.