Medical lab: Because of an intern's mistake, you were shrunk and the scientists had to abduct you, so their secrets wouldn't be leaked out. Thankfully, they're remorseful and are trying very hard to fix you, though they may do other tests on you, smelly ones.

Secret base: You have been chosen for a test subject for some super secret project and have been shrunk for this purpose. You'll be trained to become the first super solider in this project, even if you have to go through some really disgusting training.

Stranger's bedroom: You managed to hitch a ride with an unknown person as you shrunk and were taken straight to their room unaware.

Alien ship: Another abduction scenario, this time by aliens, and in the process, you shrank.

Different world: Summoned to a different world, either to a land of giants or you've shrunk (the latter more likely), you've been chosen to be the hero to defeat the evil Demon Queen, Assto. However, in order to use your powers fully, you require someone's odor.