Lunar Twins

The legend of the Lunar Twins states that the goddess Luna and the god Luan are twins that have gone on a lifelong mission of watching over the eponymous moons. Due to the different moon cycles, they have torn apart and can only reunite if both moons reach the full moon state simultaneously.
Because of this legend, the people of Etheriel began to celebrate the Lunar Reunion to honor the sacrifice of the two gods.