Star Nebula was the main base of the Galactic Star Army with mysterious origins, and while it was claimed by Sir Percival and his squad during the beginning of the war it is clear that someone else lived there beforehand. Star Nebula later became the head for where young starwarriors were raised and trained before being sent off to gain frontline training and further education. 

It's been well noted the physics of the planet don't make sense, and that it's oddly perfectly easy to defend. Around this odd satellite rotates an asteroid belt which provides a formidable defence against large warships, it's noted that in one of these asteroids is a hollow cavern with an unusual temple and several Kabus that only allows Starwarriors to enter. It's believed that warpstars come from this temple, and it's guarded by an unusual bunch of creatures dubbed guardians. They revealed to a confused and curious Percival that someone a very long time ago used a special book to write the rules of the Star Nebula, thus bringing it into existence. They stated he did so because he knew that one day the GSA would form and that they'd need a home. Where the book is now and who the creator was is unknown. While the GSA was driven out of this place when they lost the war, they later returned to reclaim and rebuilt Star Nebula, leaving behind their base on Popstar.