Serpentis is a planet inhabited by humanoid beings that worship the fire snake Werthrent, which hails from another realm. They regularly sacrifice people (either unwilling victims, or pilgrims who volunteer for this), which are devoured by the snake and trapped in an undead state within its entrails. They also worship other gods, like the goddess Sentella.
All the food on the planet seems to be made of snake and poison. Sentella, the snake goddess of good fortune, is an important figure in the religion of the planet.
When Werthrent was killed by the Team Squad after they took the Dimensional Key from hearth, the ring around the planet vanished.