WARNING: The following contains spoilers for Season 4, Episode 1 of Attack on Titan, "The Other Side of the Ocean," now streaming on Crunchyroll, Funimation, Hulu and Amazon Prime.
The final season of Attack on Titan has finally begun, and with its launch, confirmation of a key plot point. Following the release of trailers, promotional images and most tellingly of all, character designs, anime fans suspected that Season 4 would involve a time skip. The biggest clue was the redesigns of the main cast -- the Survey Corps -- who not only sported new, black ODG but had different, more mature haircuts and looked notably taller.
Though the Season 4 premiere doesn't feature Eren and Co., the reappearance of one of the Corps' former allies, Reiner Braun, is what gives the time skip away. An Eldian working for Eldia's bitter adversary, the Marleyan military, Reiner is the holder of the Armored Titan power (one of the Nine shifters). For years, he worked behind enemy lines on Paradis Island -- his race's walled stronghold -- as a double-agent alongside fellow Warriors, Annie (the Female Titan) and Bertoldt (the Colossal Titan). Reiner, a gravely wounded Zeke (the Beast Titan) and Ymir (the Jaw Titan) were the only members of the elite Marleyan Titan unit to make it back home. Annie was captured in Season 1 while Bertolt was taken down by Armin and Eren in Season 3 during the battle to reclaim Shiganshina, with Armin eventually inheriting his power.
In Episode 1 of Season 4, "The Other Side of the Ocean," Reiner and Zeke stage an aerial assault on Fort Slava, the last stronghold of another of Marley's enemies, the Mid-East Allied Forces. Meanwhile, the Marleyan army launches a ground attack fronted by the Cart Titan and the new holder of the Jaw Titan power. Winning this battle is of vital importance as it would mean the end of a four-year war between the two sides, as we learn from this season's new characters: the young Warrior candidates who are next in line for the shifter powers in Marley's possession, watched over by Commander Magath and Colt Grice.
At first, viewers would be forgiven for thinking this is an event set sometime in the past, but Reiner's subtle signs of aging clue us into where we really are in the series' chronology. Solid confirmation, however, comes from a few seemingly throwaway comments from the soldier as he gazes down from his drop ship at the Fort: "Walls... I'm sick of walls." Reiner infamously suffered the mental scarring of fraternizing with his Eldian brethren more than his compatriots on Paradis -- sometimes even losing himself completely in his fake identity. Clearly, this comment is a callback to his tortured existence there.
Given that Marley's victory at Fort Slava in the season premiere is hailed as the end of the Marleyan-Mid-East Allied Forces' war, we can assume that four years in-universe has passed between the events of Season 3 and the start of Season 4, as Marley would have been unlikely to wage such a conflict with most of its best assets elsewhere. How this small but significant jump has affected Eren's side will be interesting for anime-only audiences to discover. Last we saw of him and his friends, they'd finally identified Marley as their "real" enemy -- the source of their Titan plague. Though the Warriors' nation has just signed a peace treaty with one foe, another still lies in wait.