Founding Titan

Guidebooks put the Founding Titan at roughly 13 meters, though that ceiling seems softer than for the other Nine; the body Eren Yeager generates after receiving Ymir Fritz's full strength towers over even the Colossus Titan, and his final form, dubbed the End Titan, stretches into an enormous elongated shape whose name plays on the kanji for both conclusion and tail. Ancient Eldian artwork tends to draw the Founder clutching a war horn, possibly an artist's stand-in for the scream that triggers its power. Reiss inheritors show a stranger tell: under the sway of Karl Fritz's will, their normally pale eyes periodically darken and give off a glow.

Screaming activates everything the Founder does, and the user needs no Titan body to do it. The scream barely even has to be audible; Frieda Reiss could wipe Historia's memories through calm conversation. With it the inheritor can turn Subjects of Ymir into Titans of any scale, the method Karl Fritz used to raise the thousands of Colossus-sized Wall Titans locked inside the Walls, and can then command those Titans absolutely, as Eren discovers when he unwittingly sends a horde to devour Dina Fritz's Titan and drive off the Armored Titan. Ancient Eldia marched such Titan armies to war, and Rod Reiss believed the power, fully applied, could erase every Titan alive.

The same principle reaches into human minds. Entire populations can have their memories rewritten, which is how the people of the Walls forgot the outside world, though Ackermans and anyone who is not a Subject of Ymir stay immune. The Founder can also rework Eldian bodies themselves; a king six centuries back armored his people against an epidemic, and Zeke Yeager planned to sterilize them all the same way. Through the paths, the inheritor can speak into the mind of every Subject of Ymir at once, and can even perceive past, present, and future as one moment, nudging earlier inheritors so that history stays on the course already witnessed. Eren admits he used this to steer Dina's Titan away from Bertolt and toward his own mother, and that the ability muddies its holder's thinking.

One catch defined the power for a century: only royal blood, Fritz or Reiss, can use it freely. An outsider who inherits the Founder can still tap it through contact with a royal-blooded Titan, since the true mechanism is command over the soul of Ymir Fritz, who kept obeying her royal masters for two millennia after death. Touching a royal human instead only leaks stray memories of past inheritors. Royal holders face the opposite prison: Karl Fritz bound his successors with a vow renouncing war, an ideology that overwrites their personalities, forbids raising the Founder in Eldia's defense even against extermination, and can only be sidestepped by a non-royal inheritor borrowing royal contact. Zeke claims he alone nullified the vow from within the paths.

The story begins about 2,000 years ago with an enslaved girl. Hunted for supposedly freeing a pig, Ymir falls into water beneath a great tree, where a spine-like creature fuses to her and makes her the first Titan. King Fritz exploits her strength for thirteen years, takes her as a concubine, and fathers Maria, Rose, and Sheena; when Ymir dies shielding him from an assassin, he forces the daughters to eat her corpse so the power survives. Her ability fractures into the Nine Titans, and her spirit keeps building Titan bodies for her descendants from inside the paths.

Seventeen centuries on, the 145th king, Karl Fritz, abandons the mainland conflicts, walls his people inside Paradis Island, erases their memories, and seals his heirs with the vow. The royal line, renamed Reiss, passes the Founder down in a chapel cavern for generations, through Uri and then Frieda in 842, until Grisha Yeager kills Frieda in 845 and steals the power, later feeding himself to his own son. Eren first triggers the Founder in 850 by striking Dina Fritz's Titan in a moment of rage, then spends years concealing how it happened to keep Historia safe from those who would weaponize her blood, even as Rod Reiss tries to feed him to a titanized Historia to bring the power home.

In the war's endgame Eren reaches the Founder's full strength by touching Zeke and winning over Ymir herself in the paths, freeing her from millennia of servitude. He unleashes the Wall Titans as the Rumbling, announces the world's destruction to every Subject of Ymir, and privately tells his friends they must kill him and become humanity's heroes. The allied forces cut the head from his colossal form, wrestle away the centipede-like source of all living matter, and finally destroy the End Titan he rebuilds from the severed head. Eren's death erases the Founding Titan, and every other Titan alongside it.