|You damned coward!! Take what you got coming!! Get out here! Get out here and pay for what you've done!|
|— Keiji tries to break through Annie's crystal|
Keiji was a tall, tan soldier with a large build. He had dark hair with some lighter shades near the base of his skull, which he kept in a buzz cut. He had visible lines under his eyes and rather defined cheekbones. During missions, he was shown wearing the standard Survey Corps uniform. His civilian clothes consisted of long, dark pants, a long-sleeve short with a short-sleeve t-shirt over it, as well as a jacket that he would occasionally wear.
Keiji was a loyal soldier of the Survey Corps. He seemed to have a volatile personality, as seen when he lost his temper after Annie sealed herself inside of a crystal, repeatedly stabbing at it while cursing her and demanding that she pay for her crimes. He also seemed to be somewhat impatient, yelling at Eren for disobeying orders to stay hidden in favor of killing a Titan.
Keiji also seemed to be rather blunt in his speaking, casually commenting that Ymir was 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 Titan Forest during the 57th Expedition Outside the Walls. 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, causing Erwin to modify his plan, and order Keiji to set the charges farther back, so that they will only sever the Titan's wrists.
Before the Survey Corps can expose the Titan's nape, it attracts a group of Titans with a loud scream. Keiji joins his fellow soldiers in an attempt to slay all of the Titans to keep them from devouring the Female Titan, but they are eventually overwhelmed and ordered to retreat.
After Annie Leonhart reveals herself to be the Female Titan and transforms inside of Stohess District, Keiji and his squad pursue her, trying to stop her from escaping over Wall Sheena. However, he and his squad are forced to break off their pursuit when she begins destroying buildings, sending debris flying in their direction.
After Annie is defeated, Keiji helps remove her from her Titan's nape. Before they can take her into custody, however, she encases herself in a crystal that they are unable to penetrate. Enraged that Annie has escaped justice, Keiji hacks at her crystal with his sword until he is ordered to stop by Hange Zoë.
In Ehrmich District, Hange goes over a report about Annie Leonhart's background with a number of soldiers, including Keiji. He hears Armin, Eren, and other members of the 104th discuss whether it is possible that Reiner Braun and Bertolt Hoover could have been working with Annie.
Keiji is among the soldiers that accompany Hange Zoë to rescue the 104th graduates trapped at Utgard Castle. During the battle, Keiji berates Eren for ignoring orders to stay out of sight when the latter breaks cover to kill his first Titan in his human form.
After rescuing the recruits at Utgard Castle, Keiji returns to Wall Rose with the rest of Hange's squad. While using his maneuvering equipment to help other soldiers climb the wall, he informs Eren of the injuries Ymir sustained during the battle and muses that she would not have survived her experience at Utgard if she had been a normal human. 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 Bertolt and Reiner reveal themselves to be the Colossus and Armored Titans.
Keiji and the other soldiers scatter to avoid the Colossus Titan's attack, but he notices that one of the soldiers does not make it and is eaten by Bertolt, along with Ymir. Hange orders her soldiers to swarm the Titan, and as they dodge around its fist, Keiji notices that the Colossus Titan is slow, just like in reports. He joins the other soldiers in diving for its nape, but before they can reach it the Colossus Titan emits a scalding burst of steam that drives them back.
Hange leaves three of the four squads present to watch Bertolt and takes the remaining squad, including Keiji, to face the Armored Titan, which is fighting Eren in his Titan form. As 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. Helpless, the Armored Titan roars in desperation and the Colossus 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.
Keiji is reunited with Squad Levi, Hange, the goggled soldier and Nifa, listening as they discuss Armin Arlert's plan to seal the hole in Wall Maria using Eren's Titan hardening abilities, and as Hange reveals Nick's murder at the hands of the Military Police First Interior Squad.
Keiji 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 Keiji orders Jean to check and make sure there are no witnesses as they disperse.
After Hange kidnaps Nick's murderers, Keiji is tasked with guarding their cells. He is present when Dimo and Flegel Reeves meet with Levi, watching as Levi coerces Historia into accepting her role as the queen. He then listens as Nifa relays a message from Erwin, revealing his plan to have Eren and Historia handed over to the Military Police and track them to the location of Historia's father, Rod Reiss, the true ruler of the Walls.
After Eren and Historia are captured by the Military Police, Keiji is a part of the group taken by Levi to track them as they are transported to Rod, with Keiji monitoring them from a nearby alley. However, they are ambushed by Kenny Ackerman and his subordinates, and Keiji is shot in the head. Collapsing in the street, his body is found by an alarmed passerby.
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.
Despite never being seen in actual combat, it is implied that Keiji was a fairly capable fighter, as he survived the 57th Expedition beyond the Walls, during which he directly engaged the Titan horde that was attempting to devour the Female Titan, and a fight against the Female Titan during the capture operation in the Stohess District. He participated in the fight at Utgard Castle and against the Colossus Titan, both of which he survived. All of these facts prove his exceptional skill and reliability as a soldier.