I mean, the art predates even the one shot but it's clearly the same two characters. This is just one of those cases where the lewds predate the series.
Contrary to (warped) expectations, it seems Aoi doesn't have a brother complex. Actually good. No need to worry about a potential love triangle where both roads lead to Alabama. Just one (marriage technically legal, after some years) road.
Looks like lil sis has some kind of modeling gig going on. I guess that explains the dyed hair.
Why didn't he tell her? ...Maybe because he himself didn't know he was transferring?
At this point anime has trained me not to even enjoy looking at vaginas anymore. All my sexual instincts tell me to rub it on bellies, armpits and feet and leave the rest for men of lesser refinement.