Is it weird that books are unrated? I would never want this book censored, but it seems like we could have some indication of what to expect. If a young boy picked the book up thinking it was just some comic he might be shocked by what he saw and learned.
Content Advisory Spoiler (scroll down for it):
Ehwah learns to masturbate. It's a tasteful scene, but I can imagine being shocked if you didn't expect it. That is all.