World Trigger (Tamakoma's Purple Flash)

One day, in Mikado City, a gateway to a parallel universe had opened. From it, an outbreak of aliens known as Neighbors wreaked havoc across the city with their own sophisticated technology. Suddenly, a mysterious group of people brought themselves together to repel their attacks. Soon after, Border was formed, an organization researching Neighbor technology and maintaining a defense system against the Neighbors. Its members are armed with weapons known as Triggers. Four years later, the city has recovered from initial Neighbor attacks to the point where its civilians have become used to them. A 15 Year old boy named Tomioka Chiba, is an S-Rank Agent thats been off-duty for 4 months after his first raid in the Neighborhood and now is a current student at Mikado City Middle School.