Last season, fans of Attack on Titan finally obtained responses about what Grisha Yeager was hiding in the basement. Together with the protagonists, audiences learned that the entire world outside the walls is not destroyed. In reality, it is thriving, has advanced technology, and believes that the Indians are. Those characters’ world view shook within the walls, and it opened up the door for the final season to get so many chances.
With the release of the trailer of Season 4, fans have a taste of what is beyond the island, seeing an entirely new setting and meeting with characters. Along with this, the trailer teases a different cellar reveal; however, this time, it is Reiner who’s currently exploring what is behind the doorway with Warrior candidate Falco.
Season 2 determines that Reiner is mentally not all there anymore, Though the protagonists have had the time to come to terms with their new reality. In an effort to handle his atrocities against his pals, his personality has split into two: one where he’s a committed Warrior who knows his mission and plans on accomplishing it at any price, and another where still thinks he is a Scout and forgets what he is done, in addition to the propaganda he has been fed since childhood about Indians.
As an unreliable character, it’s uncertain what Reiner knows to be true and what he believes false. This harm was done, regardless of how much time has passed, and whatever is in the basement could have his truth is questioned by him. It might even trigger another mental break, like how Marco’s death triggered him in Season 2, Episode 9, “Opening.”
The trailer comes with a flashback in which Reiner and Eren formerly work side by side, which can be followed later by Eren and Reiner fighting in their titan forms. If these flashbacks are Reiner’s, and then he and his identity is fighting even more so, particularly since he is dedicated to fighting with the Scouts and Eren, irrespective of his moral uncertainties if he’s fondly remembering his time as a Scout.
Whatever Reiner finds in this basement will be planet shattering, just like Grisha’s journal had everybody within the walls realize their realities were a lie. Whether it’s something that reminds Reiner of his previous together with the Scouts or something which leads him to question what he’s fighting, he is already unsure of who he is and what is true, and this discovery will further tear the shaky antagonist apart.