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Keiji is a loyal soldier of the Survey Corps. He seems to have an impatient personality, as seen when hit Annie's crystal enclosure repeatedly while accusing her of paying for her crimes  and yells at Eren for leaving his position when killing a Titan.
Keiji is first seen participating in the operation to capture the Female Titan inside the Titan Forest during the 57th Expedition. He appears again after Annie encases herself in crystal during the mission in Wall Sheena and he hacks at it with his sword until being ordered to stop by Hange Zoë.
When 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. Keiji appears again with the rest of the Survey Corps fighting the Colossus Titan. After it falls onto Eren Yeager and the Armored Titan, Keiji is among those who are wounded from the impact of the blow that the Colossus Titan made when he fell off the Wall.
Keiji is not seen again until after Eren has been rescued and Levi's squad are at their new base. He sits silently with Hange, Nifa, Moblit Berner, and another Survey Corps member, while they are being told of the plan for Eren to seal Wall Maria by hardening his Titan body like the Female Titan did.Keiji is murdered by Traute Carven, a member of the Military Police's First Interior Squad, as part of Kenny Ackerman's plan. With a shot to the side of his head, Keiji is killed instantly along with Nifa and an unnamed Survey Corps member also from Hange's squad, leaving Hange and Moblit as the only surviving members of the fourth squad.
Later in the Battle of Shiganshina, as Erwin Smith begins to lament the dwindling hopes of his dream, Keiji stands among the many fallen Survey Corps comrades in Erwin's mind, wanting to know if their deaths had meaning.