104th Trainees Squad

Marco is first introduced during the initiation of new recruits, and is intimidated by their instructor, Keith Shadis, after he expresses his desire to join the Military Police. He later attempts to maintain order when the recruits question Eren about the attack on Wall Maria, which Eren experienced firsthand. He chides the others when their questions become too upsetting for Eren.

During his time as a trainee, he befriends Jean Kirstein and the two are often seen together. He seems to have been one of the only people to recognize Jean's potential, as well as spotting his weaknesses and how to improve them, and encourages him to embrace his natural abilities as a leader. They become good friends and are rarely seen without the other.

In the year 848, two years before graduation, Marco accompanies the other trainees on a wilderness hunt to sustain themselves in times of peace. Along with the other trainees, Marco is pulled into an equipment heist by thieves in the forest and is left behind with the others as Eren Yeager helps rescue the kidnapped Krista Lenz. He is seen with Reiner Braun and the others as the thieves are caught and arrested and Krista is safely returned