Infinity Wars is certainly living up to its billing as an event that will redefine the cosmic landscape of the Marvel Universe. As it's unfolds, we're more about how the Infinity Stones work (they operate in tandem with each other, linked as a circuit), while also witnessing the galaxy being graced with a new tyrant in the form of Requiem, aka Gamora after she broke bad.
However, Gamora's role in reshaping the cosmos goes way past a new identity, because not only has she killed Thanos, her adopted father, she's harnessing the power of all the Infinity Stones via a special armor designed to basically make her a walking, talking Infinity Gauntlet.
Obviously, due to her actions, a long list of enemies have begun coming after her, but while Requiem focuses on the usual suspects trying to stop her quest to change the universe, her greatest threat may not actually be who she thinks it is. There are a few folks hidden in plain sight that she's simply not paying attention to, and who she needs to keep her eyes peeled for.
The Forgotten 'Sibling'
Infinity Wars #3 has taken Requiem to the God Quarry; she believes there's something intriguing there, as she can't see beyond it even with her new omnipotence. Loki warns her about the place being a boundary for creation, that gods go there to die. Rather than heed his words, she impulsively sends him back to Earth. She's had enough of his sneaky ways, after all, and so heads to the cosmic grounds with Flowa, an Asgardian librarian she's allowing to document her proceedings.
It turns out, this is the place is where Thane, Thanos' son and Gamora's foster brother, is buried. In Jeff Lemire and German Peralta's Thanos #12, the Mad Titan attained a power-up there and decimated Thane in combat after the Phoenix Force deserted his petulant offspring. He then threw his son to the bottom of the quarry where he turned to stone, facing his own inner-demons. Requiem is now digging into this quarry, sensing a mysterious power beneath, indicating the possibility it could be linked to a dormant Thane who may have finally awakened to his true potential.
In her ignorance, Requiem might be bringing up someone who would love a chance to follow in his father's footsteps and attain all the Stones for himself. Thane has a lust to be a god, after all, and this could be the opening he always wanted. Also, he may want revenge on Requiem for robbing him of the chance to kill Thanos himself.
An Even Darker Reflection
Requiem believes she's taken her main threats out of the equation by beheading Thanos and folding the universe onto itself, mashing together everyone in the universe and thus halving all life. But in Issue #3, Loki makes a valid point as they peer into a rift in the multiverse, watching other realities where different versions of Requiem go about conquering their respective universes.
One specific fight stands out, where Phyla-Vell and Moondragon (who are both dead in the mainstream Marvel Universe), as well as Gamora, battle a Requiem. Loki points out not every Requiem necessarily has to be a Gamora, which hints that one or several of them could actually invade this reality if they chose. Sure, the Infinity Stones can only work in the respective universe it came from, but that doesn't mean a Requiem from somewhere else can't come over, claim that universe's stones and reshape yet another reality.
In short, if a Requiem from another universe took Gamora's armor, he/she could rule this universe. The mainstream Requiem seems to overlook this, as her thoughts are preoccupied with the God Quarry's mystique. But from Loki's words, the underlying threat here is that Requiem's greatest enemy could well be another Requiem, something the ghost of Thanos keeps teasing her about as he continues to haunt his murderer.