This is an extremely solid work of art. Quick, digestible plot that is easy to follow and get excited about. Predictable enough to be familiar with just a hint of mystery. Really nice additional touches, like rolling up the skirt and showing the sister's thought process. On top of everything, the art is just about perfect. The characters' expressions are vivid, appropriate, and not overdone.
I spent a few minutes trying to think about how this could be improved, but I think this is the ideal one-shot. A quick set-up followed by a burst of emotion and intimacy with a satisfying end. Good job getting Ushio Kiyoshi, FAKKU!
Iori-chan, seeking to lock Kouki-kun in place, used Entrapment .....
"IT'S SUPER-EFFECTIVE!"
Plus it seems that, all jokes and smack talk aside, Kouki had feelings for Iori, too. So then, it all worked out fine ... unless for a while they have to keep it a secret from Iori's onii-chan.