As of Bubbled, things are looking really grim for Yellow Diamond. She has now lost 8 fully-formed gems including her strongest Jasper and an era-1 Lapis Lazuli. Not only that, but two ships are missing, her planet-sized geoweapon is MIA, and worst of all…

SHE HAS NO IDEA WHAT’S GOING ON!

Now, when I say she has no idea, I literally mean she literally has no idea. She’s most likely aware that there are crystal gems on earth because of Peridot and Lapis’s reports prior to their appearance in The Return, but Rose Quartz was completely unaccounted for and she has no idea how many of the Crystal Gems have survived. As of Message Received, she’s aware that Jasper is MIA and that Peridot has gone rouge and may or may not have destroyed the cluster. The Ruby squad she sent prior to Hit The Diamond is also MIA, and they have not reported back to her since they arrived at earth. We know this because the Rubies claimed the nearest communication line was on the moon, and they were not aware that it had been destroyed.

In war, information is everything, and YD has no clue how many gems she’s fighting or what resources they have access to. Worse yet, with dwindling resources her soldiers are no longer expendable. She needs to be able to find and recover the soldiers and know what’s going to happen.

She needs Future Vision, or at least a gem who has it!

Under these circumstances, future vision is basically the most elegant solution there is. While rare, and thus dangerous to risk, future vision has two very important applications: both of which are crucial to solving the failed earth missions

The first use, seen in Winter Forecast, allows a gem with future vision to see with perfect accuracy the outcome of any chain of decisions without any real-world risk. Before executing an attack plan, a gem with future vision can live the entire plan in detail and use it both to see the lay of the battlefield and confirm the said plan’s viability. In short they will know if any play will fail before even executing it, and will be able to learn everything they would have known if they had actually done it.

The second, application, as seen in The Return and discussed in Cry For Help, and implied in many other episodes, is the ability search their possible futures for a timeline in which they find what they’re looking for, such as when Garnet used it to find Pearl and Amethyst on the hand ship, or presumably to find many of the gem monsters they caught over the course of the first season. This application would be necessary for YD to track down Jasper the Rubies now floating aimlessly through the solar system.

So, now we know what Yellow Diamond needs and why she needs it, let’s talk about what her options are. At the moment, there we only know two of them.

The first possibility is for YD to send in another Garnet, but at the moment it’s not known if there are single-gem garnets, and homeworld still really does not approve of mixed-gem fusion. That leads us to option two, the big one, the one this theory is all about:

Sapphire

Yellow Diamond sending in a Sapphire (presumably with a body guard) seems like the safest bet, but it might require a bit of clarification. While our Sapphire was a member of the blue court, and any blue sisters are presumably not out for loan, it should be noted that real sapphires come in nearly every other color of the rainbow, including yellow.

I should note by the way that Sapphire is not strictly a unique gem. As Garnet said in The Answer, Sapphire is “rare” implying that there are more than one. Now, it may seem like a risk to endanger a rare gem like sapphire, but given that the cluster, a geoweapon capable of threatening an entire planet with surrender or death, is a stake no risk is too great.

Given that her job is going to be tracking down Rubies, this could have some pretty interesting story potential, especially given that one of them seems desperately jealous of her fellow rubies getting some action

As a side note, Eyeball’s eyeball just happens to be in the same place as Ruby’s eye on Garnet. Presumably, if a Sapphire did fuse with eyeball, their stone would be right on the forehead, unless of course Yellow Diamond decides to bet cautiously by sending a Sapphire who also has an eye gem, and thus would only be able to see the future.