The Fall of Shiganshina arc

The Fall of Shiganshina arc (シガンシナ陥落弧) is the first story arc in the Attack on Titan anime.

Introduction
Inside the Walls of humanity, three children, Eren Jaeger, Mikasa Ackermann and Armin Arlelt live peacefully while dreaming about seeing the outside world someday. However, a mysterious threat known as the Titans lurks outside these Walls and the children soon learn of their terror as the Colossal Titan breaks through the gate to their home, Shiganshina District.