Board Thread:Theories/@comment-7673575-20170514071213/@comment-32026989-20170516200749

Helel ben Shahaar wrote: So, I have a theory that Titans can never be fully exterminated (like the Angry Eldian Kid would want to) simple because there isn't really a true way to kill a Shifter. If another Titan eats them, that Titan becomes Shifter instead. If another Shifter eats them, it's just a step closer to reuniting the Progenitor Titan (I will henceforth continue to use this name to refer to Ymif Fritz, and I will can the Shifter of Reiss family a Founding Titan, in order to avoid confusion). If they get killed while human (which is rather bloody difficult) the Shifter power will just reincarnate itself into an Eldian child that is about to be born. Due to all of this, it is a natural order of things that at least one Shifter exists at any given moment, and their spinal fluid can be used to make Titan Serum, which turns regular folks into Titans. Of course, seeing how Shifters are only reborn into Eldians, one could argue that t's possible to eradicate both Titans and Shifters by utterly exterminating the Eldians, but that is rather impossible.

Yup, you seem to be 100% right, according to all the info we got so far. But there might be a future plot point to end the Titans once and for all, as Duck said above, probably by uniting all 9 Titans into the "Progenitor", as you said, and then unmaking the pact somehow, or whatever Isayama comes up with.

Buuut that's just guessing. So far you're right, the Titans are impossible to be exterminated unless they just wipe out all Eldians.

EDIT: just mixed this with another theory on the other thread, and although it sound silly, it also sounds something that could actually happen: http://attackontitan.wikia.com/wiki/Thread:46289