The Demonic Lancers.

It's been known that the only way for these warriors to become stronger is to defeat each other and absorb their fallen peer's power.
The Empire discovers, through the battles held between combat slaves and monsters at arenas every day, that the Demonic Lancers' powers could actually be intensified through battles with abnormally powerful monsters and creatures that have been exposed to the energy of the Apostles like Sirocco.
So the government selects the strongest and longest-surviving combat slaves from arenas and sends them everywhere in the country to resolve the aftermath of the Metastasis, exterminate monsters, and keep the general populace happy, all the while cultivating a powerful regiment.

The Dragoons.

They are the professional monster hunters trained by the Empire. The first Dragoon and the leader of the others, Marx, who is also known as Jager, pays a visit to the Imperial lords who own combat slaves, picks out slaves who are most sensitive to Sirocco's energy, and immediately sends them to the Empire.
These slaves, unlike the other Demonic Lancers, are completely isolated from other groups and learn the monster-tracking and hunting techniques and combat arts that the Empire has secretly developed. When their training is complete, they hold a festival of their own called the Red Moon Festival, in which ten warriors who caught bigger game than the others are selected and named Dragoons and sent out to different places on the Arad Continent.