So, I've had this really wild theory the other day for the (ending of the) manga.
We all know the tree, which Eren is leaning at in the first chapter, right? Well, this tree has nine branches.
And then there is the tree from chapter 122, in which Ymir Fritz fell. down there, she "connected" to something, which might look like a parasyte, but I believe that it is one of the tree's roots.
Well this root has nine of these bigger roots on the back and thirteen of these smaller roots (9 titan powers; 13 years to live).
What if the trees from chapter 1 and 122 are the same ones or have the same origin (the root Ymir Fritz connected to).
Now, I believe that Eren somehow needs to get to this tree, to then save Ymir Fritz when she is falling down. As time in general seems to be a bit off there, this might somehow be possible.
Also one could assume that if Ymir Fritz is actually the same person as Historia's (and Eren's?) baby/child, the last panel, which we alredy know, would also make sense, as then Ymir Fritz would be free and these titan powers basically never existed.
I don't know if you actually understand what I mean haha, but I thought I might just share this theory with you guys. What do you think?