My theory about the yamaokas (long text that may acrescent nothing to your life)
iv finished the rin yamaoka archives mission today and seeing the little movie i can say WOW that gave me chills, very well done.
Getting straight to the point at the end of the animation you see rin surrounded by 3 Samurais, and that gave me 2 theorys.
The yamaokas power came from an entity deal or curse and the three samurais behind rin are brothers ( if it is a curse being brothers are ok, a deal should be strange cause its like a lightning hitting a tree 3 times cause the entity would need to seal with 3 persons of the same family in different times, but as everyone is samurai the time stamp cant be too long so i think they are brothers), also one of the three samurais is the ONI (but as i said i dont remember well the oni lore so i dont remember if he had brothers). Now talking specifically about the powers i think maybe they come from inheritance, or blessing from the ancient samurais.
1 - If it comes by inheritance i think every yamaoka family member will have a unique ability (that would be cool but as i said its a long time stamp and someone would notice superhumans in the world)
2- The power that a yamaoka family member have is the same as the ancient 3 samurais (i think this is the most accurate, but this theory has a hole and i will get there later; so the power is given to a yamaoka by inheritance but it needs to be activated, in other words is mostly like a blessing that they get if the samurais thinks they are worthy (that seems to be the case in the Rin bloodbath story).
Remembering that all yamaoka members are killers maybe its a entity curse.
In the Rins lore we have the Dragon that she says that was awaken in the sword fight, and when she was in the street with the bullies we can see THE ONI WRATH, so what i think that happened.
We have 3 basic samurais
The ONI - with wrath (the oni power basically)
The Dragon - with Proud ( i think the dragon is proud cause he always wanted to fight and not turn back)
The Spirit - With Revenge (i think this is the power that the spirit have and earned when her father killed her, i think her father did that being in a samurai influence, maybe something that the entity planned to get Rin in the trials).
the problems with these theorys
1- every yamaoka would need a power and the killers list yould be HUGE, the only way to explain the low quantity of yamaoka killer would be trying to proof that the powers awaken only with one blessing from the 3 samurais. Or maybe the yamaokas are reincarnation of the samurais.
2- If the power that the members have is the same as the samurais and the killer THE ONI is one of them, so the spirit should be one of them too, but as she lives in the future and the time stamp exists she cant be one of the three just a reincarnation or someone blessed with a samurai power from the 3 samurai in other words the original THE SPIRIT. With that said the game currently have the 1 samurai and a reincarnation from the 3 one missing the Dragon and the Proud for a future DLC release, if the devs want to release the 3 yamaoka cursed brothers would be awesome but it would still miss the original SPIRIT unless we treat her as a 4 samurai, a possession a reincarnation or release a skin in a samurai armor.
I said 3 brothers curse but one of them can be a woman and the age diferences can exist in a 100 years time stamp in the japanese samurai time.