Franz had a large build with shaved black hair. He had grayish-brown colored eyes, and a slight tan. He wore the standard trainee corps uniform, with a dark green shirt underneath.
He was a good-natured young man, only wanting everyone to get along. He was not one to get upset or anger others. But when there was a chance Hannah Diamant would be in danger, he vowed to protect her if it was the last thing he would do.
On the 104th Training Corps' last night together as trainees, a fight between Eren Yeager and Jean Kirstein breaks out. As the fight picks up, Mikasa Ackerman stops it by carrying Eren out of the mess hall. Franz also blocks Jean's path, nervously convincing him that the fight was over. Later that night, Eren passes out while trying to remember his father. Franz, with Armin Arlert and Bertolt Hoover's help, carry Eren back to his bed. He is visually worried after Eren awakes from a terrible nightmare.
The next day, Franz is walking through Trost District with Hannah and Eren. He and Hannah begin chatting, optimistic that things are looking up for humanity. Angered, Eren begins yelling at them, calling them a couple, which they both embarrassingly deny. Some time after the breach of the Trost District's outer gate by the Colossus Titan, Franz is attacked by a Titan. He is bitten in half and dies immediately. In shock, Hannah attempts to resuscitate him. After Armin has his own breakdown, he finds himself at their location. He is shocked by what he sees, Hannah calls out to him asking for help while she continues attempting to bring him back with CPR.
- Franz' name is remarkably similar to Franz Kafka, a Czech writer considered to be one of the most influential authors of the 20th century. Franz' lover, Hannah Diamant, shares the same last name as Dora Diamant, who was the lover of Franz Kafka during the final year of his life.
- In the japanese version of the anime, Franz's voice actor also dubs Sonny.