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In his Titan form, "Cartman", Pieck is 4 m tall and walks on all four limbs in a quadrupedal fashion as its name implies. His torso is long and flat, allowing for materials to be easily packed onto his back. His face is elongated, bearing wide lips and a large nose with a very small forehead and a huge mouth.
After Zeke and his army appear, Pieck is seen walking among them, acting as a mule by carrying crates and barrels strapped to his back. When Erwin Smith sees this, he theorizes that Pieck has intelligence and acted as a scout to warn Reiner Braun of the Survey Corps' oncoming approach.Erwin's theory was correct. Pieck had been watching the Survey Corps' movement toward Shiganshina District. As Zeke was conversing with Reiner and Bertolt Hoover, the Titan spoke, warning them of the Survey Corps' imminent arrival.
After the battle with the Survey Corps begins, Pieck assists Zeke by supplying him with rocks to crush and throw at the soldiers.
After Zeke slaughters most of the Survey Corps in their final charge, Levi Ackerman brutally rips apart Zeke's Titan and removes him from the nape, preparing to feed Zeke to any surviving Survey Corps member he could inject with the Titan serum. Pieck surprises Levi when it charges at him and Zeke from behind and steals Zeke in its mouth, barely giving Levi room to escape. Pieck then flees with Zeke, and the remaining Titans are ordered to kill Levi by the warchief. The two are then pursued by a determined Levi as he begins to take down the Titans and vows to keep his promise to Erwin.Pieck appears inside Shiganshina with Zeke on his back. He quickly makes his way over to Eren Yeager who is sitting on a rooftop holding Bertolt Hoover captive. He stops and stands by as Zeke and Eren speak. During this time, Zeke reveals that he knows Eren's father, Grisha Yeager. Before he can go into detail, Levi appears atop the Wall and jumps down to pursue them. Pieck then sprints away at Zeke's command.
After Reiner had been located, Pieck appears out of nowhere and lunges at Hange Zoë, attempting to crush her in its jaws; however, Jean Kirstein is able to tackle her out of the way in time. Hange quickly gets to her feet, blade ready, but is shocked when she sees Pieck holding her hostage, Reiner, in his mouth. Pieck then makes off with him and is pursued by Connie Springer, who is then ordered to stop by Hange as she believes he will just have the tables turned on him. As Levi, Eren, and Mikasa Ackerman debate over who will be injected with the Titan serum and devour the now-defeated Bertolt, Erwin or Armin Arlert, Pieck climbs and reaches atop Wall Maria with Zeke and Reiner, looking on.
Four years later, Pieck is present at the battle of Fort Slava at the climax of the war between Marley and the Mid-East Allied Forces. While it is suggested by Colt that he should engage in combat with the fort's defenses, Commander Magath denied the suggestion due to the presence of anti-Titan artillery which could kill any Titan with a single 100mm round.