"Mikumo Osamu" is chapter one of the World Trigger manga.


One day, a gate to another world opened in Mikado City (Population: 280,000). Invaders from another dimension, later called "Neighbors" trampled everything in the vicinity of the gate, spreading terror throughout the city. The Neighbors' technology was different from that of this world. The civilans' weapons were ineffective and thus rendered useless. Everybody in Mikado belived it was only a matter of time before the city was destroyed.

Then, a mysterious group suddenly appeared. They repelled the neighbors, simply stating, "Leave them to us, we've prepared for this day for a long time." They were an orginization that independently studied neighbor technology, and fought to protect our world. They called themselves the Border Defense Agency, or "Border" for short. They quickly built a giant base, and set up defense measures against the neighbors.

It has been four years since then. The gate that allows the neighbors to enter into this world is still open but surprisingly few people left Mikado City. Because they have so much faith in Border, people have somehow grown used to the occasional explosives and flashes of light.


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