The Calendar

Thieves' guild, Csipherus-based. Currently engaged in guerilla warfare versus the Red Eyes and draconian wonder twins, possibly the only reason the city is still standing. May not be strictly good, but definitely angry enough to fight.

Pre-Campaign
Set joined the Calendar after things started going south in Csipherus and it got harder and harder for him to find food. It's unclear what he had to do to join it or whether the people who stole his stolen food were from the Calendar themselves, but pretty much, he was good enough at pickpocketing and keeping watch that the group took notice of him and recruited him. Artemis Kalends was his primary teacher, advocate, and friend.

"Well, I've Lost It All, I'm Just a Silhouette" (1x54)
The party met some members of the Calendar in Csipherus when Zeno attempted to steal some of their liquor or water stores in a bar as Set was leading the group to a known hideout. They were taken down to the catacombs, the Calendar's headquarters, where they met the Keeper, a person high up in the organization, who traded information with them about what was going on in the city.

Tattoo
Each initiated member of the Calendar has a tattoo on their left shoulder that is a celestial model. In the center is a white or open circle representing the sun and then, depending on the member's deeds, a varying number of concentric circles representing the orbits of planets, as well as moons, asteroids, and other objects in space. The full meaning of the tattoos remains unclear, but a good metric is that the more stuff someone has, the more they've done for the organization/the more important they are.

For reference, the Keeper has seven rings of planets and celestial objects and Set has two.