Can't say I like Aina much. Her other side is too disgusting. Her "normal" self is pretty cute with a decent personality(depending on how jealous she is), but her pimped up self is as repulsive as they get, be it in personality or appearance. If she didn't have that off-putting second personality, she might be my favorite female character in this manga, but right now I think that either chisa or the mc's little sister gets that spot. Can't say I'm rooting for aina, she can go home for all I care. She hardly contributes to the comedy, rather, she tends to be annoying more often than not. I'm also not a big fan of romance drama in a gag comedy manga. If people get into a relationship, it should be simple and straightforward without all the romcom bullshit of misunderstadings, awkwardness, denseness and other offputting behavior.
Anyway, what is "septic couple" supposed to mean? Septic isn't really a word used to describe relationships, it's a medical term. The closest idea I can get to is "rotten couple" but that seems to be a long stretch when "septic" is used, at least no one else in the world is using it like that. Are you sure you don't mean "platonic" or some other word and mistook it for "septic"?