It's a children's tale of how the moon and sun function on a small planet and their guardians that guide them through large stone/animal across the planet each day. The guardians have to raise and drop the sun according to the time of day, and be at the correct longitute/latitudes for the time of year. The basis is how a nightcreature named Mune is accidentally picked to become the guardian of the moon without any formal training and ends up losing the moon on his first day and how he has to realize he needs to fix the troubles he's caused (the moon breaks off, the sun gets stolen, and then the moon dies). I won't spoil it, but it's a really neat origin story for a special night guardian in common folklore.