Notes:

http://www.giantessworld.net/viewstory.php?sid=6088

In quite possibly THE kinkiest fanfiction scene of all time, the already-freaking hilarious fanfic Alphys VS Undyne, during the short but bittersweet span of its fourth-through-sixth chapters, had Undyne shrink herself to insect size and then take advantage of her miniscule stature to enact all SORTS of sick, nasty fetishes on Alphys' body…

Which, of course, included but was most DEFINITELY not limited to sneaking inside her head through her ear canal and taking control over her brain, with the sole purpose of using it to publicly humiliate Alphys beyond belief for her own sadistic sexual amusement.

Ironically enough, however, Alphys VS Undyne is actually one of the best and funniest Undertale fanfics ever written despite all of this, and also largely because of it:

https://www.fanfiction.net/s/12052538/1/Alphys-VS-Undyne