The main reason I put the game at 16+ is that I know that content like depression, self-harm, substance abuse, blood, etc. (while not all necessarily in CH 1, are all possibilities) can be a lot for some people. But with that said, in this VN I don't think I'll get to a point where it's so heavy that I think a 16 or 17-year-old couldn't handle it and know their limits with having been given a warning. I do however acknowledge that sometimes things shift, and while I do have the outline for the story, I don't have every small detail figured out.
There's a possibility that there will be more graphic (blood/gore) content down the line, as well as the possibility that the aforementioned heavy themes get to be a lot more intense (especially considering they, most namely mental illnesses, are kind of the main topic of fell). If I get to a point where I think that the people reading really really should be in a good place before reading, I will probably make the game 18+ and give even further warning, but I really just don't know at this point if that will happen.
As for the topic of NSFW content, at no point have I ever really considered it as a possibility. So to answer that portion, no I do not currently intend to have NSFW content in Fell.
P.S. I'm glad you enjoyed chapter one, my friend.