Royal Guard Drones:
There are two sources of Royal Guard drones.

Lunaris and her mages make every effort to capture and rehabilitate Solar Flare’s drones when they can. However, sometimes they have been drones for so long or have been subjugated to so many mental spells that there is nothing left to save. In such cases, everything is fine for them that can be, and then they are given a new purpose to serve in the royal guard. Loyalty to the queen and royal family is implanted in them and they are given new life as guard drones.

The second source is prisoners convicted of level 4 crimes. Such prisoners are subjected to thorough indoctrination and brainwashing, molding them into loyal guard drones who desire only to serve their queen.