http://segaretro.org/images/6/6a/V5_md_jp_manual.pdf
In the story section, there's definite reference to an alien in the latter part; I don't think such references existed in the story made for the arcade release. Granted that even Japan-side, this was produced by Tengen, but I'm not sure if that means they added story elements Toaplan never intended. Anyone care to translate it for us?