The older sister seems to be a bit unnecessary. I mean her character helps you understand why Koiko tries so hard to be normal but aside from than that she just seems to be a bit of a nuisance honestly. I would have preferred that the sister that lives overseas or in another prefecture. But I guess we're going to get a lot of development out of her.
The sister weird me out tho
i dislike her attitude and her "principles" seems like she will become a huge nuisance in the future
hope she won't get in her sister's way, that would be fucked up