The basic story is that Yuki is going through voice mutation due to puberty, and of course Atsushi finds this incredibly… erotic (his words, not mine). So, obviously, duh, this leads to them fucking. Which is technically the main content of this side story - but the illustrations are basically them laying on each other half-clothed for few panels, barely even showing anything anyway. That’s it.
It doesn’t have any real story and it skimps even on the fanservice it was obviously intended to be.
An excuse for a sex scene followed by an excuse of a sex scene.
