Moon

The Moon, also known as Lua, Tsuki, and Luna is the Earth's moon and the setting of most of Spark the Electric Jester and Spark the Electric Jester 2.

Background
Originally, Formies were going to call the moon Luna, after the Luna Base in Mare Desert. However, they found records from old civilisations of different names for the planet and decided to use all of them. Because of this, the name of Spark's planet isn't mentioned often, as there are simply too many names to list.