you could just impliment a show or hide NSFW system? Ive seen some artists do it where if you click SFW, it will take a set of code and the story will run as if meant to be sfw only, while on the flip side, toggling NSFW would use a seperate set of code and the story would then read off the more adult lines as if always ment to be NSFW.
it basically means, writing two seperate sets of text.
this can also, influence the people who tend to be completionists to try both so they can get a unique perspective of each toggle.
up to you, but it may help you. in this context, you could leave the game as labled 18+, and ask the rerader which experience they prefer when they launch the game