Royal Weapon (5e Equipment)
From D&D Wiki
Weapon (any weapon), rare (Attunement: Special*)
Royal weapons are magical items with marvelous decorations and inscriptions, it is given to royalty and their followers as a sign loyalty and honor.
All royal weapon gain a +2 bonus to attack and damage rolls with these weapons. However, a royal weapon can't simply be taken or attuned to by simple means, it must be given by its previous owner to another person deemed worthy by him, or else the new wielder must succeed a Charisma save throw (DC 18) so that it doesn't gain a disadvantage when attacking with it.
While attuned to this weapon, you gain proficiency with Charisma (Persuasion) skill. Your proficiency bonus is doubled if you are already proficient with that skill.