World Trigger: Borderless Mission

One day, a gate to another world opens in Mikado City (三門市, Mikado-shi) and monsters called "Neighbors" (近界民（ネイバー）, Neibā; lit. 'Near-world people') start appearing from it. Humanity struggles to fight the Neighbors, as their weapons are ineffective against them, until a mysterious organization appears that is able to repel the Neighbors' attacks. The organization is called the National Defense Agency, or "Border", and has appropriated the Neighbor technology "Triggers", which allows its user to channel an internal energy called Trion and use it as a weapon or for other purposes. When a Trigger is activated, the user's body is replaced with a battle-body made of Trion.

Four years following the appearance of the gate, the people of Mikado City have become accustomed to fighting with the Neighbors and have mostly returned to everyday life. One day, a mysterious white-haired student named Yūma Kuga (空閑 遊真, Kuga Yūma) transfers to the local school. Kuga is actually a strong humanoid Neighbor, which he seeks to hide from Border. At school, he meets another student, Osamu Mikumo (三雲 修, Mikumo Osamu), who is secretly a C-rank Border trainee. Since Kuga is unfamiliar with life in Mikado City, Mikumo must help him adjust to life there and keep him a secret from Border.

World Trigger was the 20th best-selling manga of 2016, with over 1.2 million copies sold. By July 2023, the manga had over 15 million copies in circulation.

The series ranked 43rd on the 2014 "Book of the Year" list from Media Factory's Da Vinci magazine, where professional book reviewers, bookstore employees, and Da Vinci readers participate; it ranked 33rd on the 2015 list; 31st on the 2019 list; 44th on the 2021 list; ninth on the 2022 list; and 26th on the 2023 list.