Introduction Arc

The Introduction Arc is the first arc of the series.

Characters

 * Osamu Mikumo
 * Yūma Kuga
 * Yūichi Jin
 * Chika Amatori

Trion Soldiers

 * Bamster
 * Mole Mod
 * Ilgar
 * Vander
 * Rad

Triggers

 * Raygust
 * Scorpion
 * Asteroid
 * Kogetsu
 * Bagworm

Neighbor Attack
In Mikado City, monsters known as Neighbors began appearing through gates and attacking the city. Nothing seemed to be able to defeat them, and many people died or went missing during the invasion. Suddenly, an organization defeated the Neighbors using Neighbor technology called Triggers. The organization, called Border, was then planted in Mikado City with their primary goal to defend the city against Neighbors.

A Meeting of Fate
15 year-old Osamu Mikumo is sitting in class when he hears of a transfer student coming to his school, which piques his interest. Meanwhile, Yūma Kuga, a student who will be studying in Mikado City, is hit by a car, but is mysteriously uninjured. As he went to the Border headquarters before school, he arrives late. While he introduces himself to the class, a student points out that he's wearing a ring, which goes against school dress code. A teacher informs him that he cannot wear his ring at school, but Yūma states that it's a memento of his father. Being intimidated by Yūma's eyes, he reluctantly allows him to wear it. Another teacher there assigns Osamu as his guide. During reading time, a bully throws several paper balls at the back of Yūma's head, telling Yūma it's a Japanese greeting. Yūma appears to understand, and squishes the paper even harder, and flicks it back at the bully, knocking him off his chair.

After school, Osamu chides him for striking back, saying it's best not to do anything. Yūma finds this surprising, stating that where he comes from, if one didn't strike back, they would be attacked further. The bullies then reappear in a larger gang, forcing Yūma to come with them. Osamu objects, prompting the bullies to take him along with them and lead the two to a Neighbor-prone zone. During a brief scuffle, Yūma breaks one of the bullies' foot. The others proceed to attack him, when a gate opens and a Bamster Neighbor appears. All the bullies manage to escape, except for the one with the broken foot. Osamu rushes in to save him, changing into a Border uniform, revealing his status as a Border agent. He attempts to attack the monster, but cannot break through its skin with his sword Trigger. Yūma joins the fray, revealing that he possesses a Trigger, in the form of his ring. He easily defeats the Neighbor.

After the battle, Osamu asks Yūma about his Trigger, with Yūma stating it was his father's. He also reveals that his father wasn't part of Border. Osamu expresses surprise, since only Border Agents are allowed to have a Trigger. Yūma then reveals that he is a Neighbor.

Japanese Customs
A team arrives at the scene where the Neighbor attacked. Someone tells one of them that there were no teams in the area, leaving him to wonder who could have done this.

Meanwhile, Osamu questions Yūma about his Neighbor status, and Yūma then says to forget everything he said. Yūma holds a large amount of money and asks Osamu if he could buy anything with it, attracting the attention of people around. Two men appear Yūma demanding money for a "broken leg". Osamu begins to tell Yūma that they were lying, when they assault him. They now demand the money from Yūma, who proceeds to break one of the gangsters leg, deeming it a trade-off, and giving them the money.

Osamu goes off to buy food when another gang approaches Yūma. A member of this group states that his father was ill, and needed the money. Yūma said that he would, but if they were lying, he would attack them. They agree, but Yūma's Side Effect determines they are lying and attacks them. Osamu chides Yūma once again for being too aggressive, and tells him that he would teach him Japanese customs. Yūma thanks Osamu and begins to walk across the road during a red light, only to be hit by a car. Due to his Trion Body he survives the impact.

See More

 * Black Trigger Retrieval Arc
 * Rank Wars Arc