Royal Heirs is a technology in Age of Empires II HD: The African Kingdoms that is unique to the Ethiopians and can be researched at the Castle. Once researched, it provides a creation speed boost to their already rapidly-deployed unique unit, the Shotel Warrior. Royal Heirs halves their base creation time from eight seconds to four seconds.
Royal Heirs is a sound choice for players who prefer to use their Shotel Warriors as emergency troops due to the Ethiopian unique unit already has a very fast deployment rate, though it can also provide a substantial tactical advantage to players who build their auxiliary Castles close to the enemy's base by letting them create massive amounts of infantry in a short time to overwhelm their opponent.
Theoretically, Royal Heirs could benefit players who frequently launch raids and worker line harassment attacks, though unless the enemy faction builds its resource camps far away from its main base and army, this is generally cost ineffective and unreliable due to the risk of retaliation.
To players who prefer standard rank-and-file units, Royal Heirs is practically useless.