Spoiler: Chapter 133
Show
On the airplane, Onyankopon informs the alliance that the fuel tank is only half full but he intends to get them to Fort Salta no matter what. As they talk about how to take down Eren, Armin says that the best option is to nuke him with the Colossal Titan but only as a last resort, he'll talk to him first. Levi points out that killing Zeke might end the Rumbling too (since Eren activated it through him) like Hange suggested, however they don't know where Zeke is. Jean and Connie state that they understand what Reiner went through now and that they're the same (having all slaughtered their friends). Reiner says that he heard the same thing from Eren on the night of the raid at Liberio and wonders if Eren wants them to stop him. The group notes that they're still able to transform and use their Titan forms despite Eren having control over them which is strange.

Suddenly the group are all drawn into the Paths Dimension. They all cry out to Eren, including Armin saying the killings can stop and they can have peace, and Connie saying he understands now that Eren was grieving when Sasha died. Appearing in his child form, Eren finally responds and says that he's not going to stop the Rumbling and he's not going to gamble with Paradis's future. That he took away the world's freedom to achieve his own. However he was not going to steal the freedom of the alliance which is why they still have the ability to transform. They're free to try and save the world but he's free to keep moving forward in his plans, and says that if neither side stops they'll inevitably fight. Armin asks why he brought them there and Eren responds that it was to tell them that there's no need to talk and that the only way to stop him is to kill him, and that they are free to do so. The group are brought back to the world and Reiner remarks that he might have been right that Eren wants them to stop him, with the group wondering what they were going to do now that they cannot bargain with him.

We next see the ship with Kiyomi and Annie talking, with the former lamenting her hand in the events. Annie thinks about her father, Eldian and Paradis comrades and last of all, Armin, saying that it's too late to do anything. Falco and Gabi appear with Falco saying he had a dream/memory from Zeke. Gabi asks her about how the Female Titan was able to gain abilities from other titans by eating them and Annie confirms it saying they experimented a lot since the Female Titan didn't have any special abilities. Falco then notes how he became a titan due to consuming Zeke's spinal fluid which caused him to take on some of the Beast Titan's traits and that his memory was one of flying above the clouds and feels that he can do the same, that long ago there must have been a winged Beast Titan, with Gabi saying how his Jaw Titan resembles a bird much unlike Porco's, and that he intends to use this power so they can fly to meet the others.

We then cut to a train approaching Fort Salta and it's revealed that Annie's father Mr Leonhart is still alive and holding the Marleyan train driver hostage, and that their plan is for all the Eldian and Marleyan survivors to use the airships to escape the Rumbling. We also see that Falco's parents, Gabi's parents, Reiner's mother and Pieck's father are also alive and on the train. Suddenly they see most of the airships take off from Fort Salta, and worse, the Rumbling has arrived nearby. They then realize that it's a bombing fleet and that they're planning to attack Eren and the titans from above.

-

As a side note, there were a few clues towards the Beast Titan being able to achieve a bird form and Falco being given flying abilities from it, some subtle and some more overt:

  • Aside from his name being Falco and his Jaw Titan looking like a bird, when we first see Falco he's looking up at birds in the sky.
  • In the aftermath of Fort Slava at the start of the Marley arc, the head of Marley's military, General Calvi (the guy who looked like Mads Mikkelsen) sarcastically commented on the possibility of a flying titan.
  • Marley's Titan Science research is only a century-or-two old compared to how much longer the Eldian Empire had the power of the Titans, so Marley may not have gotten lucky enough to get any kind of flying titan at all during their reign.
  • The intro of Season 2 of the anime showed many other giant animals besides Zeke as his ape titan. I once thought it might have been part of a general 'Beast' theme showing the Beast Titan overrunning humanity, but it might have been pointing at this in plain sight too.
  • The Uprising arc showed us many serums used by the Royal Family, including a "Strongest Titan" serum which Rod Reiss said would turn Historia into a powerful titan, and which also turned him into a gargantuan abnormal titan which was twice as big as the Colossal Titan after he consumed it. Eren consumed an "Armor Braun" serum which granted him hardening abilities like Annie and Zeke had (did it possibly come from a member of the Braun family in the past?). Along with a "Normal Titan" serum being given to Armin - all thus showing more manipulation and possible powers being taken from one titan shifter and given to another.
  • Zeke being shown with a toy monkey as a child. While it points towards him becoming the Beast Titan as we know at that point, it could also mean he has an affinity for monkeys which influenced his form.
  • Also Zeke's Beast Titan predecessor Tom Xaver said his Titan form wasn't useful in war (part of why he was only a Titan Researcher rather than a Warrior), which is strange given the combat prowess of Zeke's Beast and how he was able to brutally subdue Reiner's Armored Titan before the Battle for Shiganshina, so Xaver may have had a different Beast form.
  • Lastly the clearest indicator by far is the mural shown for the Great Titan War which outright depicts the Beast Titan in the back of the mural as a giant horse rather than an ape, hinting that it can manifest as more than one kind of creature. We know it's not symbolizing the Cart Titan because that one is also shown in the mural as a giant man on all fours carrying boulders on its back, in front of the War Hammer Titan. Link here: https://attackontitan.fandom.com/wiki/Great_Titan_War