Akuma appears to be a super-powered version of Akuma.
His full official name is Kuruoshiki Oni which means "Mad Demon". Due
to his training and meditation, Akuma may have suppressed some of the darker
aspects of the Satsui no Hado, allowing him to control his actions. As Oni,
when he finally becomes one with the Satsui no Hado, its power has now managed
to completely overtake him.