Void 4 and Black Hole are just the first two of many villains who are fighting against each other for the world's destiny. And heroes capable of stopping them are nowhere to be found.
Void 4 is an unstoppableOne-Man Army who fights alone against the combined might of Black Hole's army and every other aspiring villain in the universe. Of course, he's still an irredeemable evil bastard himself.
Multiple villains from different factions decide to beat the crap out of each other in order to prove who is Eviler than Thou, until Void 4 show up, and they have an Ultimate Showdown of Ultimate Destiny and no heroes are there to stop this showdown from occurring ...
Void 4 and Black Hole are two bullies fighting for playground control.
Unlike Black Hole, Void 4 has lines he won't cross. He wants to rule Gundalia with the help of his magical girl army, not eradicate all life in it!
Even if their goal is the same, their methods and ideology are completely opposite. For example, Void 4 a powerful sorcerer who wants to shape the world into his personal Utopia using magic, while Black Hole is a mad scientist who wants to purge the world from lesser lifeforms and replace them with machines.
Alternatively they have the same goals and morality, but said goals would put them in direct competition. Neither can be trusted for a team-up, so competition will come up.
Void 4 decides that he wants to join the side of the magical girls to redeem himself and becomes The Lancer to them in the process.
Void 4 and Black Hole are pretending to fight in order to let the hero's guard down, and in reality allying with one another.
Double Subverted: Void 4 then absorbs all the magical girls' powers to defeat Black Hole and his army, but loses his sanity in the process, making him the True Final Boss. In the process he ends up killing all of the heroes, leaving only other villains to try to stop him.
Parodied: Void 4 and Black Hole try to outdo each other by trying to do the most wicked act ever done in human history: Stealing a book.
Invoked: Void 4 eliminates all the heroes that dared to oppose him early on, so he can concentrate completely in his fight against Black Hole, who's far more powerful than any of his previous foes combined.
Exploited: A Glory Seeker "hero" decides to wait until one of the villains has killed the other, so that he can easily defeat the exhausted victor and declare himself as savior of the world.
Defied: Void 4 decides to make an alliance with the Precures to take down Black Hole. He still plans to fight against them later on, but Black Hole is a dangerous menace to all of them, and way too powerful to be defeated using only his resources, so this is the most pragmatic alternative. After Black Hole is defeated, Void 4 then fights the magical girls with his minions, only to be defeated. Void 4 then accepts the magical girls as his new friends. the magical girls then give him a new phone as part of their friendship, and they tell him that he can call them for help anytime, even though he is a Noble Demon.
"I don't care about what you cynics think: The world NEEDS heroes! Otherwise, the planet will be consumed in the flames of war when the evils of the world start fighting against each other"
"If you see Black Hole fighting an Anti-Magical Faction, don't even bother calling in the All Stars until you know that the faction has weakened Black Hole, or that Black Hole has exhausted himself fighting the faction.