The "bottom up" keyword is currently a red NSFW keyword, but there are over 550 "sketchy" wallpapers with this keyword.
Example: https://wallhaven.cc/w/95owd8
(notice that this wallpaper is merely sketchy, yet is also Bottom up)
I think the act of inverting a picture or person alone doesn't make a photo NSFW. But if the person is bottomless or otherwise revealing, that certainly does make it NSFW.
Please consider making this keyword only be Sketchy (yellow).