Thanos Hid It In Nebula
Here’s a theory that flips the whole search for the Infinity Stones on its head. We’re all assuming the Soul Stone will be the one that Thanos is after the most, but what if it’s actually the only one of the Infinity Stones he already has hidden away? What if the Mad Titan used his adoptive daughter Nebula to house it?
This theory comes from Redditor @thunderman175 and runs with the fact that Thanos routinely upgraded Nebula with cybernetic enhancements during her upbringing. It’s possible that the Soul Stone was inserted into her body during these procedures. The idea is that it can also be supported by that T.H.A.N.O.S. theory. If A becomes Amulet (for the Eye of Agamotto) and H stands for Host (the Aether needs a host), then N could be Nebula. We do agree that makes more sense than the dubious N=Necklace theory.
Likelihood: Nebula plays an important role in “The Infinity Gauntlet” storyline in the comics, so there is that on this theory’s side. However, would Thanos really prefer Gamora over Nebula if she was the receptacle of such a prized possession? Surely, he would dote on her or at least keep her close?