Spoiler for Ending: All the titans are pieces of Ymir that were broken up by the
https://i.redd.it/sgk7hq75jka31.jpg. Eren is the attack titan that is Ymir's will. The attack titan is the titan that "moves towards freedom". The coordinate is Ymir's mind.
The female titan is her female essence. Etc. The Attack titan is the titan that fights for freedom – YMIR'S FREEDOM. Clearly, Ymir is a "slave" for centuries. The attack titan's programmed role is to return Ymir's "Freedom" or will. Once Eren returns Ymir's will, she will rebel against the royal family's commands (Zeke).
Last panel of the series - https://comicbook.com/anime/2018/11/18/attack-on-titan-manga-final-panel-finale-spoilers/ is a picture - https://media.comicbook.com/2018/11/attack-on-titan-spoiler-1144885.jpeg of an adult holding a baby, with the words "You are free." The person who is free is Ymir. Free from her multi century/thousand year curse.
The exact details of how the manga will end might be a little different, but this will be the general idea of where the manga is going.
General Idea:
*Each titan was created by the original 9 inheritors each consuming whatever corresponding part of Ymir.
the guy who became the founding titan: her brain
attack: arm heart
warhammer: the other arm?
colossus: leg
female: breast
armor: ribs?
cart: foot/toe
jaw: jaw
beast: her...hair?*
The royal family eating Ymir - https://i.redd.it/sgk7hq75jka31.jpg
Note: The 3 girls eating Ymir were Sheena, Maria and Rose
*Theory: Ymir was actually an Ackerman, and here we see a Fritz having his children and some of his allies throughout the world eating Ymir.
Ymir likely had devoted her entire life to protecting the Fritz after acquiring her power, but, eventually, Fritz started to fear her and decided she had too much power for just one person to possess, so he split it among the 9 people seen here.
As someone in the release thread pointed out, her being an Ackerman explains her eternal slave-like loyalty to her own murderers. That’s the curse of Ymir, that she has to protect those who used and disposed of her for all of eternity.
Her being an Ackerman also explains why the Fritz/Reiss ended up fearing future Ackermans and decided to wipe them out; perhaps due to a suspicion that the Ackerman still resented the Fritz after what they did to Ymir.
Also interesting to note how genuinely remorseful Uri showed himself to be to Kenny and his people.*