Illun

I love how you worked that one out, taking the two colors of her outfit and then incorporating the last bit of her head and arms as the 'button'.

To break it out sort of like you do with this, one version of how I envision it happening is first the woman's legs and arms drawing up into the torso, then second her head and neck melting down and backwards while her back arches and her torso shrinks vertically, then third the head and shoulders disappear into the region behind the breasts while the torso compresses further, aligning so that the remaining torso is behind the breasts. The fourth would show the torso almost fully absorbed, and the fifth would show the base of her torso flush with the back of her breasts. I'm not sure which would be better after that, leaving the lower region on the back of it like that, or having it melt in making a smooth surface on the back, but either way with just a little connecting tissue between the two breasts. With the final view, perhaps a thought balloon coming from it that reads "Wait a second, the antidote said to take orally. Oh crap..."

If you'd like to try it with an anime character, Kuriko Kazetsubaki from Maburaho is probably the perfect candidate. She works with magic and did use it to increase her attractiveness, so she's someone who would try a magic pill that might have this effect. On top of that, she's already well endowed, so there's plenty of 'material' to work with.