So in chapter 86 we find out about Eren's father's past before he came into the walls. We come to understand that Grisha was apart of a race of people punished for the actions of their ancestors, who used the titan power to rule over the other humans. Because of this Grisha and his people are treated like how Jews were in Nazi Germany. they had to an arm ban with a symbol on it, showing that they are Eldian. Grisha also informs us that outside the wall the world is more technologically more advanced then the walled kingdom, including airships. One day Grisha and his little sister leave ghetto where they live to see an airship land without permission. they get caught by two officers and Grisha is beaten up for breaking the rules while his escorted back to the ghetto. Grisha's sister never returns home and is found dead the next morning. Grisha grows up to become a community doctor for the Eldian people while still harboring a grudge towards the officer whom killed his sister, even though no evidence to ever prove it. While treating a man, Grisha was recruited to join the eldian recovery corp., an organization formed to bring the people of Eldia back to power. Grisha didn't hesitate to join after finding out the truth of his sister's murder and pledged to bring the ruling government down. The most interesting thing, in my opinion, is that we finally find out the origin of the Titans and location of where Eren and others within wall are and how the walled kingdom came to be. The walled cities were built on an island called "Island of Paradise" and everyone living there was a part of the eldian race. Finding out the all the people in the walled cities are actually exiled members of a superhuman civilization was kinda cool.
EREN HAS A BROTHER?! Well sorta kinda half brother. Grisha ends up falling in love with Dina Fritz, a descendant of the royal, and baby boy named Zeke. The government in power starts drafting soldiers out of the eldian ghettos to fight against the eldians on the island of paradise within the wall by drafting children from 5 to 7. The drafting process was very selective because each chosen candidate would have be a proper vessel to inherit the power of the Seven titans, titans who were given special powers from the original Titan. Grisha made his son join the military in order to infiltrate the enemy lines with a spy, but was later betrayed by Zeke shortly after joining the military. So I'm wondering if Zeke is Reiner or the ape titan guy since it seems like they've inherited the powers of the seven titans. I can't wait for the next chapter.