This has already been proposed in topic #8936. An agreement was somewhat reached, but nothing was done in the end.
At the moment, on Danbooru you can't reach artworks with completely naked characters. The current definition of nude is:
The state of being unclothed. On Danbooru, this means the character's full torso, chest and back from neck to crotch, is uncovered by clothing.
This means that to find artworks where a girl is wearing nothing, you would have to do at least a nude -detached_sleeves -thighhighs search.
This thread will mainly be to discuss on what does and doesn't apply as "completey naked" (Do accessories count? How much does a body need to be shown? etc.), before moving on with gardening.
(In particular i would like to take into consideration artworks like post #4073959, where the POV male is completely naked, but the focus is on the female clothed character.)
We could also take a different route on this: forum #91355 suggested to rework the nude tag itself, essentially making it become completely nude. (This would also make the various naked_* tags more useful...)
A third option i also want to raise would be to make an unclothed tag, and maybe have completely naked implied to it, if it's implemented. This would apply for characters that are "not wearing anything, but are still not completely nude". This way, artworks like post #30300, that wouldn't count neither as completely naked nor as nude, despite effectively not wearing anything, would still have a tag to be grouped into for easier search. (although at the same time, that would just be a naked_* search...)