I don't care much for visual novels, but I've had it explained to me that a few are basically full and good stories, with a random sex scene or two that are forcibly inserted in places such that if you removed those scenes you would have no idea they were there in the first place. The analogy was that they were like dance/musical numbers in bollywood movies - appearing at random and then things proceeding as if they never happened - but I don't know how good that analogy is.
And this is why I cringe when people demand 18+ versions
Go watch porn or....whatever it is you older people do for that stuff. Don't go and ruin a fine story.