It's probably like
@Salah WG theoried, where IMU has a series of powers which he
lends out to Gorosei and HK alike, Gunko's arrow being the same "tail" IMU used against Sabo.
Belo empowers randos' wills.
IMU gives them discount DF powers without the need for a DF.
In the final battle, as IMU gets cornered, he will sacrifice all his Gorosei/HK henchmen and reabsorb all the powers, turning into his equivalent of Moriah's Shadow Asgard.