Attack On Titan: What Exactly Is That Gross Worm In The Finale?
Coming in at a massive 85-minute run time, the last episode of "Attack on Titan" is rife with moments that mark it as the definitive ending of the long-running saga. From Mikasa Ackerman (Yui Ishikawa/Trina Nishimura) killing her childhood friend, Eren Jaeger (Yuki Kaji/Bryce Papenbrook), to the devastating final cost of The Rumbling, it was a series finale that checked all the boxes while also subverting expectations.
Still, the series finale of "Attack on Titan" was not without its resounding questions. Perhaps most cryptic of all is the nature of the worm-like creature that escaped from Eren's body after his Founding Titan was decapitated. While we first see the worm in Season 4, Episode 20 ("To You, 2000 Years from Now"), its origins are never explicitly stated.
What we do know is that it's the source of not just Ymir Fritz's (Chiyuka Miura/Apphia Yu) Founding Titan, but of The Nine and every subsequent titan in existence. Sometimes referred to as the "source of all living matter," it's a primordial creature that had slumbered in a massive tree for countless millennia before Ymir finally discovered it and gained the power of the Founding Titan.
There is no way to know with certainty what the worm was
As a young girl who was cast out from her village in ancient times, Ymir Fritz wandered the forest until she found the giant tree and entered the opening at its roots. There, she came into contact with the centipede-like organism and set events in motion that would define the history of Paradis, Marley, and the entire history of "Attack on Titan."
Unfortunately, there is no 100% clear answer as to what the source of all living matter is. Like the island in "Lost" or the Black Lodge in "Twin Peaks," it's deliberately vague despite its importance to the story of "Attack on Titan." Still, the moniker that it's often known by, as well as a few flashbacks, suggests that it was around when the first organisms came to life on Earth and is possibly responsible for every living creature on the planet as a result.
Despite its endless power and mysterious origins, though, the worm is killed after Ymir accepts death and Eren's head is severed from the power of the Founder. As such, the organism that caused the events of "Attack on Titan" is wiped out, as are all titans, and humanity must return to a more traditional form of warfare, which, unfortunately, it inevitably does. Still, the final scene in the series finale sees a young boy entering a familiar-looking tree — an ending that hints that the whole cycle will once again begin anew.