An Impertinent Rookie
Yuma joins Round 2, armed with a new Option Trigger. Meanwhile, Arafune Squad finds itself hounded by Mikumo Squad and Suwa Squad. Arafune goes back to his roots as a former Attacker and uses the Attacker Trigger Kogetsu. What will Osamu and Chika do?
Aired 09/08/2015EP 41 - An Impertinent Rookie

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)