A stroll down memory lane
Here, Eren and Zeke are free to wander through the past; remember, time and space don’t have much meaning in the Coordinates. Zeke takes Eren to visit their father Grisha Yeager’s memories to prove that they were both equally brainwashed by him. Zeke visibly looks shaken to see that his father abandoned the rebel cause against Marley to spend a peaceful life with his family, which is very different from the Grisha he remembered.
Flashbacks reveal that Grisha found the Reiss family basement long ago, but did not take any action. On the day Wall Maria collapsed, he finally decided to take action against the family, thereby putting into motion a complicated plan to topple Marley’s control of Eldia. But that would require killing the Reiss family children, which he hesitated to do. In one of the biggest plot twists of the show, we see an enraged Eren, observing his father from the future, admonishing his father for having second thoughts. Then Eren using his titan powers to take over Grisha, forcing him to kill the Reiss family.
Yeah, it was Eren all along.
Pushed by Eren to the edge, Grisha manages to murder the Reiss family and capture the Founding Titan. After the slaughter, Grisha briefly gets to see Zeke through Eren’s memories and profusely apologizes for being a terrible father. He begs Zeke to stop Eren from destroying humanity.
The Founder Ymir and the origin of Titans
Next, we find out the true identity of Ymir, the Founder. Contrary to the monstrous picture the Marleyans had painted of her, she actually led a very woeful life. She was a mere child when the Eldians captured her village under King Fritz and turned everyone into slaves. After a pig from the farm goes missing and Ymir is blamed, she is hunted by royal guards till she falls down a hole in a tree.
In another important reveal, we see the origin of titan powers. As Ymir falls into an underground lake through the hole, she comes in contact with a parasite that closely resembles a real-life species called Hallucigenia. The first titan ever emerges from the ground.
King Fritz decides to use Ymir’s titan powers to expand the Eldian empire and wreak havoc on the rest of the world, including Marley. The atrocities committed by Eldia pave the way for two millennia of hatred and lead to the current bloodbath happening in the world outside Ymir’s plane.
King Fritz uses Ymir as his concubine and she gives birth to three daughters: Maria, Rose, and Sina. The walls of Paradis were named after them. Ymir sacrifices her life to save King Fritz from an assassination attempt. In a few moments of animation, a lifetime of pain flashes across Ymir’s eyes.
The viewers are left to guess whether she was bound and destined to serve Fritz, or somehow chose to out of love and affection. Maybe she hoped that after giving her king everything, including three children and her life, she would get some honor in death.
Such was not her fate. King Fritz, reluctant to give up his greatest weapon, chops up her body and feeds her to the three daughters. Ymir, meanwhile, gets stuck in the endlessness of the Coordinates for eternity. She becomes entrusted with the job of building and re-building Titans at the beck-and-call of the royal family, a slave for eternity.
The Rumbling
Back in the Coordinates, when Eren whispers in Ymir’s ears that she is free and a slave to nobody, it is the first time someone treats her like a human being. Breaking the bonds forged over 2,000 years, Ymir grants Eren the body of the massive Founding Titan, the final form of Eren Yeager.
There’s no stopping the Rumbing now.
Eren breaks out all the Colossal Titans in the walls of Paradis and leads them to march over the world. He makes his intention clear in a message broadcast to every single Eldian through the Coordinates. “The Wall Titans will trample every inch of the world beyond this island until every last life beyond our shores is wiped out.” The way Eren figures it, that’s the only way Paradis Island will be safe from outside forces who wish it harm.
Things go berserk in Shiganshina as several things happen simultaneously. Armin nearly sacrifices himself to stop Connie Springer from feeding Falco to his half-formed Titan mother. Armin, Jean, and Mikasa are forced to kill Commander Pixis, who was now a pure titan after Zeke’s scream.
Meanwhile, by thawing all the trapped wall titans, Eren also thaws out Annie Leonhart, who has been crystallized since the end of season 1.