To all the guys being creeped out... You do remember that Chapter 1 started with Otone explicitly saying that she and "Onee-san" are dating, right? Hell, Chapter 2 and 3 begin with a profile page after their respective covers that repeats that information. That should've been your cue that they would be doing unambiguously sexual stuff sooner or later.
you'd almost think some sub to her work just so they can be creeped out by it. There's several tags I'm not a great fan of, but to make life easier for me and those who do enjoy it, (I just don't read it)