|Go for it, Eren! Tear the head off his neck! Pull the traitor outta there!|
|— Keiji encourages Eren during the latter's fight with the Armored Titan|
Keiji was a tall, tan soldier with a large build. He had brown hair, which was beginning to turn gray in the back, which he kept in a buzz cut, brown eyes, and had rather defined cheekbones. During missions, he was shown wearing the standard Scout Regiment uniform.
Keiji also seemed to be rather blunt in his speaking, casually commenting that Ymir is not normal due to her Titan abilities while speaking with Eren, seemingly unconcerned with how Eren, an Intelligent Titan himself, would feel.
Keiji is first seen participating in the operation to capture the Female Titan inside the Forest of Giant Trees during the 57th Exterior Scouting Mission. Commander Erwin Smith calls him to prepare the explosives to blow off the Female Titan's hands, which are protecting its nape. Keiji expresses concern that doing so would also blow up whoever is inside. Erwin takes his input into account and modifies the order to amputate the wrists instead.
They stop in Ehrmich District where Hange goes over a report about Annie Leonhart's background with a number of Scouts, including Keiji. He hears Armin, Eren, and other members of the 104th discuss whether it is possible that Reiner Braun and Bertholdt Hoover could have been working with Annie.
Keiji is among the soldiers that accompany Hange Zoë to rescue the 104th cadets trapped at Utgard Castle. When, during the battle, Eren ignores orders to stay out of sight in favor of killing his first Titan in his human form, Keiji berates him for breaking cover.
After rescuing the recruits at Utgard Castle, Keiji returns to Wall Rose with the rest of Hange's squad. As the heavily injured Ymir is being lifted to the top of Rose, Keiji muses that, had she been a normal human, she would not have survived her experience at Utgard. After Hannes brings word that there is no hole inside of Wall Rose, the soldiers prepare to return to Trost District, but are stopped when Bertholdt and Reiner reveal themselves to be the Colossal and Armored Titans.
Keiji and the other Scouts scatter to avoid the Colossal Titan's attack, but he notices that one of the soldiers does not make it and is captured by Bertholdt. To his surprise the Colossal Titan eats both the soldier and Ymir. Hange orders her soldiers to swarm the Titan. As they dodge around its fist, Keiji notices that the Colossal Titan is slow, just like in the reports. He joins the other soldiers in diving for its nape, but before they can reach it, the Colossal Titan emits a scalding burst of steam that drives all of them back.
Hange leaves three of the four squads present to watch Bertholdt and takes the remaining squad, including Keiji, to face the Armored Titan, which is fighting Eren in his Titan form. Eventually Eren gains the upper hand and traps the Armored Titan in a hold that threatens to tear its head off. Keiji hangs off the Wall with the other soldiers and shouts encouragement to Eren.
The Armored Titan roars in desperation and the Colossal Titan responds to the signal. It plunges from the top of the Wall to land on Reiner and Eren, creating an explosion of steam. Keiji is burned by the scalding winds and is laid out among the unconscious wounded on top of Wall Rose.
Fully recovered from his injuries, Keiji reunites with the rest of his squad and Levi's squad. He takes part in Hange's experiments on Eren's Titan form, observing the tests from a distance. When the strain begins to damage Eren's body, Hange ends the experiments and orders the soldiers to disperse. As they leave, Keiji orders Jean to check and make sure there are no witnesses.
After Hange discovers that Pastor Nick has been murdered, Keiji accompanies her to inform Levi and his squad. Shortly after bringing the news, Nifa arrives with a message of her own from Erwin, which prompts Levi to order everyone to evacuate the premises.
Once safely evacuated, Levi reveals that a freeze has been declared on all Scout Regiment activity, and that they have been ordered to hand Eren and Historia Reiss over to the government. At Levi's request, Hange places Keiji, Nifa, and Abel under his command so that they can help smuggle Eren and Historia into Trost for safe harbor with Commander Pyxis.
Entering Trost, Keiji is tasked with transporting a covered wagon hiding Eren and Historia to Pyxis while Levi's squad uses decoys to try to carry attention away from them. On the way to the Garrison's headquarters, the wagon's way is barred by citizens trying to get food rations from the royal government. The wagon is attacked by members of the Military Police, and Keiji attempts to escape with it. Eren and Historia are both knocked unconscious during the escape and Keiji, momentarily distracted by their plight, is killed.
Despite never being seen in actual combat, it is implied that Keiji was a fairly capable fighter, as he survived the 57th Exterior Scouting Mission, during which he directly engaged the Titan horde that was attempting to devour the Female Titan. Furthermore, in the 57th Exterior Scouting Mission, Keiji was part of the team entrusted with guarding the Female Titan. This implies that he was among the few Scout Regiment members who knew about the true objective of the expedition, meaning that he had managed to stay alive for at least the past five years and that he was a trusted member of the Scouts.
- Keiji's appearance underwent an extensive redesign in the second anime recap movie; his brown hair was darkened, his widow's peak and his cheek bones were made less prominent, and streaks of gray were added to his hair to better match his appearance in the manga.
- These changes were retained in the second season of the anime.