>>281264512 (OP)She's meant to be rounder.
That said, the mistake of this manga is precisely to only have one couple, young one at least, there's the old geezer.
The author introduce plenty of couples but waste all its time trying to make "nana&kaoru" feel like a deep romance.
It would have been mure more interesting to have several couples, all thinking they are pervs, unaware half of peoples try out bondage, and each of them would have a different kink on the spectrum.