imminent penetration
When vaginal or anal penetration is about to occur, but hasn't happened yet. This includes "regular" sex, the use of sex toys, tentacle sex, fingering, or any other type of sexual penetration.
This tag is for nude characters, use dry humping or bulge to ass for clothed situations.
Don't use this tag if you don't see penetration about to occur. Images like Danbooru post #4204975 or Danbooru post #4557040 shouldn't have this tag because penetration may be circumstantially implied, but isn't visibly about to occur.
If the penetration is non-consensual, tag imminent rape, as well.