There's actually full-frontal nudity in the game, so it kind of IS adult -- no sex, but you definitely see nipples and even pubic regions on some of the defeated bosses as you progress (and said bosses turn into cute anime girls when you defeat them), so it's pretty borderline. By modern standards, it would be rated M for Mature by the ESRB here in the U.S. -- not AO for Adults Only, since there's no actual sex -- but back in its day, it would definitely have been classified as an adult title.
As for the manual, I can try to scan it for you at some point. I'm moving to Japan in about 2 months, though, and have most of my MSX games packed up in boxes to eventually be sent to me there -- but I was considering busting some of them open anyway to play around with some of the games before I go, so I can look for that one when I do.
Incidentally, I may have a few other game manuals I could scan for you. I haven't checked, for example, but I'm willing to bet you don't have scans of any material from SystemSoft's "Robo Crush" on your site -- but I have a near-mint copy of that game I snagged off of eBay a few months back that I'm playing through now, and holy hell is that a bizarre yet amazing game. 
-Tom
Yes, thanks! And hope to see more rare scans! 
