That Did That To That

 is the 1st chapter of the 1st volume 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 felling that something is wrong, but Mikasa thinks he's 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 Colossal Titan, is introduced. It's 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 were bullied because of Eren's outburst.