The Orbital Knights are 37 clans^A) that all live in what is left of the Moon in the Orbit of Earth. In theory, they are loyal to the Imperial Family of Vers, but in practice, they are only loyal to themselves, and will willingly betray the family if they feel like it.
They are highly militaristic, violent and trigger-happy. To be fair, sitting on the Moon for about 20 years far from home and close to the enemy would drive anyone insane. Doubly so if the enemy has easy access to water, while Martians constantly deal with water shortages.
Why would they stay on the Moon? Because they couldn’t get home after the Moon had an unfortunate accident. That, and they want to be ready for another invasion of Earth.