Ouroboros
Ouroboros is a secret organization founded by Tsukiko. It is based out of The Wandering Tavern, and its members typically carry Ouroboros Pendants which help to hide them from the gods. Their exact motives are a closely guarded secret, however they can often be seen spreading strange rumors, and are excellent at avoiding close scrutiny.
After Natsu joined the Divine Council, the mission of Ouroboros changed slightly. Instead of being dedicated to robbing from all the gods equally, it is now dedicated to "stealing from wealthy assholes". The interpretation of this description tends to include every god except for the ones Natsu is aligned with, but Ouroboros is not above robbing Natsu's allies (or even Natsu herself) if events warrant or they want to make a point. Proceeds are used to keep the organization afloat, purchase new equipment, and sometimes donated to the poor, the homeless, or to The Moonlight Covenant.
