WARNING: The following article contains spoilers for Injustice vs. Masters of the Universe #5 by Tim Seeley, Freddie E. Williams II, Jeremy Colwell and Wes Abbott, on sale now.
The Injustice Universe is a place where one day you're a hero, and the next you're a villain. It's also somewhere you can literally be taken out in the blink of an eye by a fellow seeker of truth and justice. Case in point, Billy Batson, the hero Shazam, who had his brains fried by Superman for questioning his regime's violent ways.
But the Man of Steel has, at times, shown a modicum of mercy when it comes to dispatching heroes who oppose him. He really doesn't see imprisonment as putting one's best foot forward, but he will make an exception for one or two folks, as long as they matter to him. Well, one of these superheroes has made a return from a desolate prison in the Injustice/He-Man crossover, and she's ready to protect the multiverse again -- Supergirl.
Supergirl was one of the biggest draws in the Injustice 2 video game and its associated comics. Kara For-El's backstory remained more or less the same, painted as Superman's cousin who was sent to Earth when Krypton was destroyed. Of course, with Brainiac as the main villain, threatening to bottle Earth like he did her home planet of Kandor, it's no surprise an adult Kara readily wore the symbol of the House of El and fought alongside her cousin.
The catch, though, was he tricked her into thinking Batman's Resistance was evil too, using the sadistic Wonder Woman and cruel Black Adam as her mentors. Luckily, Bruce Wayne brought Kara back to the light, and after Brainiac was defeated she realized she had to stop her fellow Kryptonian. Sadly, he already planned for her betrayal, and as soon as the Collector of Worlds went down Superman acted against her and the Dark Knight.
This video game ending is what this alternate-reality crossover with Prince Adam and the army of Eternia is based on, and at the start of this series we saw Batman's fate. Superman turned him into the Black Oracle, using Brainiac's technology to enslave Bruce and source premeditated crime in society, a la Minority Report. The game's ending had Kara imprisoned in a cell with red sunlight weakening her, but we didn't find out exactly what her cousin planned to do with her. He made it clear he wasn't going to kill his own blood, and this comic then revealed he imprisoned her in the Phantom Zone.
However, in Issue #5, Batman and Superman finally broker peace when they realize Skeletor and Darkseid are about to unearth magical weapons on Eternia that could reshape the multiverse. With time against them, Batman makes it clear they need an equalizer; a wildcard the Lord of Apokolips hasn't prepared for: Kara. Superman's reluctant to bring her back from the Phantom Zone, but eventually, when we see this new alliance from Earth attacking Skeletor's armies, Supergirl is back in costume and turning the tide.
It's a desperate move for Kal-El, because deep down he knows the Phantom Zone was her biggest fear, which means she'll be coming for him once they defeat Darkseid and company. It also gives Batman a trump card, because he knows that this partnership is temporary and Superman will be trying to enslave them all as soon as the war's over. As we see her swatting away Darkseid's minions, it does become obvious she thinks Batman freed her, not Kal-El.
With one issue left, we're eager to witness her confronting her cousin once again to garner revenge for being marooned in that cold, scary prison. As it stands, now might not be the best time to oppose him, though, because Superman just got the powers of a god right after Darkseid and Skeletor fell in battle. Then again, Kara does have one advantage: She's got a Batman in her corner, which could make her the most dangerous Kryptonian in the galaxy.