The seven deadly sins's captain disappeared shortly after the ten commandments. After having a massive power surge come from another world gives Merlin, the boar sin, has enough information to make a spell to travel to the world of where the surge came from. Merlin uses the spell sending the remaining six of the seven sins, along with Elizabeth and Elaine, to Equestria to find their captain. But something goes wrong in the process, and the sins are scattered across Equestria. Merlin finds herself in a small town called ponyville, a quite fitting name considering all the residents are ponies.

Merlin is in chapter 1
Gowther is in Chapter 2