Underdepth - an Underwater Undertale

An alternate universe for Undertale, in which the underground is plummeted beneath the oceans. This will be following the pacifist route very closely!
DISCLAIMER: As well as the usual "I don't own Undertale or its content" spiel, I also make a few assumptions as to how the game goes.
Frisk is female, and a teenager.
The run is a pacifist run.
This story may contain spoilers for all three endings!