I remember seeing this scene play out in a youtube video. I had assumed it was the usual overly touchy big sister bonding scenario from the CG alone. Didn't expect for Enshou to molest Enjutsu to the point of reaching orgasm.
Found the video again, this scene starts at 25:40.
I want to see more of Enjutsu cosplaying as Sousou, she looks really cute in that outfit. Hopefully we'll see an updated version when these new Koihime games start being released, they look like alot like they might be updated rebuilds of the first two games but time will tell.