|Fear not, Your Lordship. Should he face the Titans on a real battlefield, the commander will not need to be as lenient with them.|
|— Gustav to Wald|
He is a tall, young man of a solid build. He has combed brown hair and dark brown eyes. He wears the typical Garrison uniform.
Gustav is portrayed as a stern, quiet individual. He seems respectful to his fellow soldiers such as Armin Arlelt, which can be seen when he listens to his plans and takes his opinion into consideration.
When the 104th Cadet Corps participates in a mock defense of Trost District, Gustav monitors their progress alongside Anka and Pyxis. He later helps Anka oversee the cooking contest that Pyxis is judging.
Gustav appears in the residence of Lord Wald, accompanying Dot Pyxis along with Anka Rheinberger. He watches as Pyxis plays chess, losing on purpose, seemingly to satisfy the Lord. At that moment, a soldier barges into the room, announcing that the gate in Trost District has been breached by the Colossal Titan, much to Gustav's surprise. Wald protests that Pyxis will not be able to defeat the Titans if he cannot even win a game of chess, to which Gustav callously responds that Pyxis will not allow the Titans to win in the same manner that he allows Wald to win.
Later, he comes in time with Pyxis to stop Eren Jaeger from being executed. Dot Pyxis creates a team to formulate a plan to recapture Trost, Gustav is included in that team. He later hears a plan from Armin and states all the risks. He tells Armin that if the central part of plan remains unknown, then it is like leading soldiers to their death. He is later seen telling the commander about the soldiers who had been "lost" during their mission. Commander Pyxis replies that they had not died from being lost, but because he had ordered them to do so and would gladly accept punishment of a mass murderer if mission fails.
Gustav attends Eren Jaeger's trial along with Anka at Pyxis' side.
Gustav is accompanying Pyxis when the Vanguard reports back that there is no breach in Wall Rose, and informs them of Reiner Braun and Bertholdt Hoover's true identities as the Armored and Colossal Titan.