Red Kingdom Agana
The Red Kingdom is predominantly Oriental and Asian influenced. The kingdom is basically ruled by a clan which is the noble main bloodline of the kingdom. The Main bloodline Head is the leader more commonly known as the emperor or empress, who have retainers which are the extended family. There are ninjas and samurais in this kingdom rather than normal soldiers.
Originally the Red Kingdom were part of the Blue Kingdom and are considered outcasts and rebels for being tempted by the Dark Kingdom's influences of sacrificial summoning and practiced the Dark Arts of the Black Kingdom, which was considered forbidden in the Blue Kingdom.
The humans were thrown out and made their own kingdom based off their newly summoning abilities which they call the Blood Contract, where they engage with an Oni permanently by offering and sacrificing their blood to the Oni, so the Oni would forever serve the family bloodline for generations, and began an alliance with the Black Kingdom.
To summon an oni, one must have an oni in possession.
There are several ways to get an oni however.
Oni can be only called upon and feed off their master's blood unless ordered by the master to consume another oni or another human being. However the master's blood is the most sustaining for the oni.
Oni make a contract with the summoner to be forever loyal to the blood of their master who summoned them, and thus it is extremely rare for an oni to ever turn on its master.
Oni Ranks - Kudans
Most children are tutored by personal teachers. Summoning oni is not something that can be taught easily to multiple individuals at the same time as it involves discipline and self-harm that can vary from individual to individual. Also depending on the family, some teachers teach combat abilities. Others may only teach necessary summoning basics.
Samurai and ninja
Many fighters become either Samurai or Ninja based on their family background and skills. Samurai were usually noblemen who became soldiers who served the Emperor. Ninja on the other hand are mercenaries, bought for their services.