The climax of Chapter #110, Eren escapes from his prison cell and fully commits to separating from the Survey Corps. But why did Eren escape his cell?
Eren chose to escape his cell because he wanted to meet Zeke. The military was planning to choose someone more agreeable to inherit his Founding Titan, so Eren’s sympathizers helped him escape and hold control of the Founder’s powers.
He escaped using the Warhammer Titan to open a hole in his cell. Eren then covered his tracks behind so he could not be followed and met with the Yeagerists some distance away.
Chapter #110 | Eren Escapes From His Cell
Following General Zackley’s assassination, the higher-ups from the Survey Corps, Military Police and Garrison Regiment were summoned.
Hange Zoë, Commander of the Survey Corps, explained that a bomb was installed in Zackley’s custom-made chair. Including the general, four other soldiers were killed. She vouches that Anti-Marley volunteer Onyankopon has been with her all day before Armin remembers an important detail about the chair.
Zackley asked “new recruits” to help him move the chair, Armin explained. Shortly before Mikasa and Armin entered the General’s room, they saw some suspicious new recruits who were just leaving headquarters. He identifies them as from the Survey Corps.
The room goes cold. Nile Dawk, Commander of the Military Police Regiment, reveals he heard the rumor that those who were punished for leaking Eren’s information were part of the Survey Corps. Suddenly, a messenger bursts into the room, yelling that Eren Yeager escaped from his underground prison cell.
Eren Yeager escaped from the underground prison! He used the power of the titans to create a hole in the prison wall to escape! He also covered the hole so that we could not track him! Get all the soldiers to search for him!
Military Messenger to Room | Chapter #110
Armin and Mikasa are in shock to hear the news. They both quietly realize that with this act of treason, Eren may have pushed himself so far away that he can’t peacefully come back again.
Eren Joins Up With The Yeagerists
After an unknown-distanced walk from the prison, Eren meets up with the Yeagerists. A group of Eren sympathizers, the Yeagerists explain to Eren their behind the scenes moves to better his position.
Floch, former Survey Corps member and now active advocate for Eren, introduces the group.
We have more members, including the ones that aren’t here. The prison guard that rescued us from prison, and the prison guard that allowed us to meet here right now. They are inside the military right now, hiding.
Floch to Eren | Chapter #110
Floch explains how Darius Zackley was assassinated because the military wanted someone they were comfortable with to inherit the Founding Titan.
The scene ends with Eren’s only request to the Yeagerists: locate Zeke. Once Eren and Zeke make physical contact, he’ll be able to use the Founder’s power as he sees fit without obstruction.
That’s the short answer. Eren chose to escape his cell because he wanted to reach his brother, Zeke. The military was circling in on feeding Eren to someone they trust, so the Yeagerists helped him escape from the prison cell.