The rarest charm is the "day one" charm.The rarest wrap is the "Dark matter" wrap it can only be unlocked when you get 100 thousand kills on a weapon so ar get 100k kills you have it but only on ar nothing else.The rarest finisher is "diamond hands" to get this you need to have 50k kills on a weapon and it only goes on the weapon that has the kills.The rarest skin in rivals is "RPkey" and it is lower that 0.01% and not even possible to obtain anymore.
The rarest skins are key skins and the key skins are AKEY-47 Keynade Key Bow Kitana Keyvolver and 2 more