Attack on Titan: Junior High - Season 1 Episode 1 Starting School! Titan Junior High School

On the very first day of junior high, Eren oversleeps and is woken up by Mikasa. While rushing to school, he runs into several of his classmates. When they arrive at school, everyone except Eren notices something is odd. They realize that they walked into the Titan side of Attack Junior High School, and are later introduced to their class 1-4 properly by Hannes. They attend the entrance ceremony, only to find that their principal unleashes Titans to crash their entrance ceremony.