A Sound Argument

In his cell, Eren mutters at a mirror to keep fighting until Hange interrupts, insisting they never believed he would let Historia be sacrificed. The story steps back two years to the Paradis port, where Kiyomi Azumabito of Hizuru arrives as the island's first foreign guest. She shows Mikasa a familiar crest, the match to the tattoo on Mikasa's wrist, and reveals that a shogun's child, friendly with Karl Fritz, was stranded on the island after the Great Titan War; Mikasa is the lost heir of Hizuru's ruling line. Kiyomi credits Zeke for brokering the meeting, recalling how he handed her Miche Zacharius's ODM gear and dangled iceburst stone, the fuel found only on Paradis, as the resource that could restore Hizuru's fortunes.

Kiyomi then outlines Zeke's three-part plan: demonstrate the Rumbling with a partial test to cow the world, build up Paradis's military with Hizuru's help until the threat becomes unnecessary, and preserve both the Founding Titan and a royal-blooded Titan, with Historia inheriting the Beast Titan and bearing as many children as possible during her thirteen years. Hange balks at billing future generations for the present's survival, Historia quietly accepts, and Eren erupts, refusing to treat the queen like breeding stock and demanding another way. A year later Hizuru's greed shows: it will not broker trade for Paradis, preferring to monopolize the island's resources, and the world finds it convenient to keep Paradis as its common enemy. Hange resolves that the Scouts must go meet the outside world themselves, seeding the Liberio infiltration. On the train home, Eren's friends bicker over who should someday inherit his Titan until he cuts them off: he wants none of them to shorten their lives for him.

Back in the present, Eren tells Hange about consuming the War Hammer Titan and its remote-projection power, boasting that no cell can hold a man who cannot be killed without losing the Founder. Elsewhere, Historia sits pregnant on a farmhouse porch; over dinner, Military Police officers argue about her, with the drunken Roeg wanting Zeke fed to her immediately and Nile Dawk countering that childbirth is dangerous enough without a Titan transformation on top. Below them, Greiz fetches wine from Nicolo's cellar. Eren's friends, blindsided by Pyxis's arrest of the Volunteers, weigh whether Eren has truly sided with Zeke; Conny raises the possibility of cutting him down, recalls Sasha's death, and asks why Eren laughed at it, a question Mikasa cannot answer. Armin proposes that he and Mikasa speak with Eren directly, noting the serum stockpile gives them the option of passing the Founding Titan to someone they trust. In the Titan Forest, Zeke's guards share wine while Levi watches him.

Kiyomi Azumabito opens formal contact between Paradis and Hizuru and identifies Mikasa as the shogun clan's lost descendant. Zeke's three-point plan is laid out: a test Rumbling, militarization backed by Hizuru, and royal inheritance of Titans through Historia and her children. Eren openly rejects the plan. Hizuru's refusal to mediate trade pushes the Scouts toward infiltrating Marley. Historia is revealed to be pregnant, stalling her inheritance of the Beast Titan. Eren, holding the War Hammer Titan, declares himself impossible to imprison, and his friends begin planning how to respond, including transferring the Founder by serum. The wine that guards keep drinking quietly threads through the episode.

The tenth episode of Season 4 and 69th overall, produced by MAPPA, adapts the chapters Visitor and A Sound Argument from the War for Paradis arc. Kaori Makita directed and Hiroshi Seko wrote the script; it aired in Japan on February 15, 2021 and in the US on March 21, 2021. The title nods to Nile Dawk's argument against forcing a pregnant queen to inherit a Titan. The episode's information segment profiles Hizuru, a small eastern nation led by a shogun, rich in engineering talent for weapons and aircraft, a onetime ally of the Eldian Empire whose shogunate crest bears three single-edged swords.