Akuma is a demon who has not yet appeared in Devil Beater, but his name and several possible concepts surrounding him have been mentioned several times.
The first reference to Akuma made was when Diablo Bufon claimed to have been revived by making a deal with Akuma, in a realm he calls "super purgatory" where time flows approximately four times slower than the real world. The second reference occurred when it was revealed that Akuma is a rival of Ineur, who wishes to defeat him through the ongoing corruption in the space-time continuum.
Anyone who visits or sees Akuma will be tainted with a signature from him. At the end of Act 35, Nick Nebula modifies Keith's demon rod, which allows him to trap and severely injure anyone who has a demonic signature. Gardi Nakara claims that the power would have to be temporary since most of the Alliance had visited Akuma, which could render all key members dead in a heartbeat. If Akuma's signature is visible to the naked eye, the mark may take the form of the silver rings that most characters wear, considering that despite the fact that they wear these possibly priceless heirlooms, there is no other implication to financial status whatsoever.
Akuma also means Devil in Japanese making it possible that because of the game's name "Devil Beater" that Akuma might turn out to be one of the final bosses of the game.