The Captured Osamu
Yuma, Chika and Xeno take the fight to the enemy in order to rescue Osamu. However, a cunning trap separates them, forcing Yuma into a one-on-one fight against Giev. A Trion soldier generates a mysterious virtual world where Yuma faces an unexpected foe.
Aired 13/12/2015EP 58 - The Captured Osamu
World Trigger
One day, a gate to another world suddenly opens in Mikado City. Aliens invincible to Earth’s weapons, called “Neighbors”, start coming over. Earth’s only line of defense is a mysterious group called the “Border” who are armed with weapons called “Triggers”.
Four years later, the city has recovered from initial attacks and citizens of Mikado City have started to get used to the Neighbor’s attacks. Yuma Kuga, a transfer student, and his classmate Osamu Mikumo find themselves fighting a Neighbor that suddenly appears. Osamu, who is actually a Border agent, activates his Trigger but is unable to defeat it. This leaves Yuma to activate his own Trigger and defeat the alien. Yuma reveals that he is not part of Border and is actually a Neighbor who has transferred from the other side.
(Source: Crunchyroll)