I've had this idea in my head for a while, one where the mc (as legitimate crown prince) has a power mix of both aura/qi and haki, by that I mean the versatility of haki and the overall style of qi/aura, meaning it isn't invisible and shares his cheat in a way. Also each person's colour depends on their preference or house colours.
There are 4 tiers to this power:
Tier 4 - only available to the monarch, married partner and crown heir after swearing an oath to be competed leaders.
Tier 3 - available to those that swear an oath to bend the knee to the royal House, also the oaths are different, meaning the remaining royal family members oath, Kingsguard oath, small council members oath
Tier 2 - no one has to swear any form of fealty to the royal family, but can't use this power to harm servant and member of nobility and royalty, or just the royal house
Tier 1 - entry level, also only those with a neutral to positive alignment can access theses powers.
And now the actual powers available(at their peak):
Tier 4 - have all 3 types of haki, have enhanced body and mind, poisen resistance, have greater energy control as a bonus, full weapon and body coating + advanced styles.
Tier 3 - have main two types of haki, conq haki is devolved to battle intent, better body and mind, minor poisen resistance, have average energy control as bonus, full weapon coating + semi-advanced styles, minor body coating, and lastly each oathtaker have a nice little bonus tailored to which oath taken.
Tier 2 - have main two types of haki, full weapon coating + standard styles, bare minimum body coating.
Tier 1- just starting get a feel for haki/qi and how to manipulate it.
And even if mc dies, this new power system will remain, helping solidify the royal power and the mc as the wise Prince. Also each can be hinted that the gods choose the mc herald this power to the masses and added the Tier 1 condition cause of the mc, to help slaves to freedom and the like.