That Did That To That

is the 1st chapter of the 1st volume and the 1st chapter overall of the Attack on Titan: Junior High manga, written and illustrated by Saki Nakagawa.

Overview
Five years earlier, Eren Yeager and Mikasa Ackerman are walking in the forest. Eren gets a feeling that something is wrong, but Mikasa thinks he is using it as an excuse to "explore." Five years later, in present day, Eren and Mikasa are about to enter their new school. At the entrance ceremony, their head teacher, the Colossus Titan, is introduced. it is at that moment that Eren has a flashback to events that happened five years earlier. With rage building within him, he yells out what the Titan took from him. For the next couple of days after the ceremony, Eren and Mikasa are bullied because of Eren's outburst.

Summary
Five years before junior high, Eren and Mikasa explore the forests, unauthorized. Eren uses the oddness of the atmosphere as an excuse to explore. He hears a sound elsewhere and finds the source, then starts screaming.

In the present, Eren and Mikasa make it into Titan Junior High School. Eren swears he will surpass the Titans, but before he continues speaking a Titan-sized eraser hits him on the head. Angered, Eren declares that he will make the eraser into a stamp which irks the Titan who dropped his stationery. Later, he and Mikasa head to their classes where they line up in separate lines differentiating from human to Titan. Mikasa notices that Eren sneaks into the Titan line, where he can get revenge by stealing something out of their backpacks. Eren steals a pair of undergarments. Due to the sheer mass of the item, Eren is crushed by it. He attempts putting it back after forcing himself out. Unfortunately, Eren is caught by a staff member and the staff member pushes Eren to apologize to the Titan student whom he stole their undergarments. Eren turns white from embarrassment and lays with his head low throughout class.

At 10:30, they attend their entrance ceremony. Eren tries sneaking in the Titan crowd, but Mikasa urges him not to and suggests he should stop with his obsession of Titans. They are introduced to their head teacher, the Colossus Titan at their entrance ceremony. This triggers Eren's memories from five years ago, and Eren reveals that the head teacher stole his bento lunch. For several days, Eren and Mikasa are bullied because of Eren's outburst at the ceremony.