Chapter 77 is out!!
I have so many thoughts right now. First, it seems like the titan shifters belong to another race, because Reiner told Annie about them hating that race, I that made me come up with a theory that I will explain later. But damm, Marco's death was really sad, they just left him there...
Now I'm really wondering if the titan shifters are actually the bad guys, they keep talking about leaving that cursed and hopeless place, it seems like they come from a place where there isn't that much chaos, but for some reason, they want the coordinate. Also, the Beast Titan said let's put a stop to this cursed history.... I don't know, I really feel like they know the big picture and what they're doing is to end that apocalyptic world.
So I have this theory... I believe the titan shifters came from a place where humans have knowledge of what happened to the world, unlike the people inside the wall that have been brainwashed by the first king. So, since the titan shifters know everything about the outside world, they should probably know how to end all that chaos and obviously, they know everything about titans, including how to turn humans into titans.
So, the coordinate power was handed to the first king and the first king decided to put humans in a cage and live fearing titans, but we all know that the coordinate's power didn't affected Asians and they were repelled. So I believe the Asian race managed to survive outside the wall and they created a village or city in there.
Of course, they must really hate the people inside the walls for the decisions they made, the Asians probably believe that all the people in there are like the first king and his religious followers. So that explains why Reiner talked so nasty about the race inside the walls, because the titan shifters are the Asians that could not be affected by the coordinate's power.
Since they know that the people inside the wall have somebody with the power to control titans, they must believe that is their chance to save humanity and they don't trust the humans inside the wall with that power. So they start sending warriors to take the coordinate, first it was Grisha, Eren's father, but he took too long, so they send Reiner and the other titan shifters, but they also took too long and then, they send the big gun, the commander, the Beast Titan.
So far that's my theory, I can't wait for the next chapter!!