You see no reaction from the guy.

That's because he's seen and experienced much more than just that, courtesy of the sisters, of course.

The OVA just seem to get more and more explicit as they are released... With that in mind, I can't imagine what's going to happen next.

... Translation request?

Here's a translation =

SFX : 'Flip'

Yep, needed a good translator to understand that cryptic language... Those damn moonrunes.

if i was keita, i would nail the both of them until i died from exhaustion

You're gonna be doubly exhausted considering how hard it was to even read the translation. That shit was a doozy, eh?