What the hell?! Are you guys kidding or trolling here?
There is nothing even 
close to NTR in here so far! Can't you make a difference between a clear 
voyeur (which it is) and NTR (which it most definitely is 
not).
The best description to Japanese genre netorare (NTR) that I have found is written (and illustrated?) by Japanese anime fans who most likely are the most competent people on the matter:
	
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Please, read it and stop throwing around terms that you are clearly not familiar with. There is way too much confusion around it already. NTR is not a simple thing to describe or understandand, the term should not be used in a light-handed manner as you seem to be doing.
There are no equivalents, no synonyms to netorare in any European language or culture and this is why you must read the long description of the genre and avoid any over-simplified definitions. It has been used mistakenly so many times already, it has to stop!
In this case, all of the three main components, main conditions are missing here. They aren't even in a relationship of 
any kind besides being siblings and roommates!
There are only a few voyeur scenes in this game. Three, if you count that bathroom peeping scene in. And one sex scene with the neighbour.
A slutty sister who likes to be watched by her brother while she's having sex. And a brother who 
likes to watch. They both 
like it. That's 
voyeur. Live and learn.
There is no sexual relationship, no cheating, no jealousy, no components of NTR.