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World Trigger Wiki
This page is about Chapter 1. For other uses, see Osamu Mikumo (disambiguation).

Osamu Mikumo (()(くも) (おさむ) Mikumo Osamu ?) is Chapter 1 of the World Trigger Manga.

Short summary[]

In Mikado City, Yūma Kuga transfers to the Third Mikado City Middle School, where he meets Osamu Mikumo and gets in trouble with the class' bullies. When Osamu and Yūma go home together, the bullies challenge Yūma to a fight, but Osamu tries defending him, getting beaten. After Yūma breaks the leader's leg, a Neighbor attacks. Osamu, revealing to be a Border agent, tries to defeat it but is thrown away. Yūma then takes on the Bamster with his own Trigger, quickly defeating it. After the battle, Yūma reveals that he himself is a Neighbor.

Long Summary[]

The chapter begins as an unknown Border agent stands above a large monster he just defeated. He calls out to the boy he saved, Osamu Mikumo, asking if he's alright.

The history of Mikado City is narrated, where a gate between another world suddenly appeared four years ago. Monsters called Neighbors began to pour out and destroy the city. A mysterious group appeared and saved the city. This group created an organization called Border to defend the world using Neighbor technology. After 4 years, the situation in the city is stabilized, and although gates are still opening, the citizens learned to convive with them, as they feel safe with Border around. In this situation, at Mikado City's Third Middle School, Class 3-1, a group of bullies teases a boy in class, throwing his pencil case back and forth like a volleyball. Osamu, who was sitting quietly until then, intervenes and returns the pencil case to its owner. He overhears some of his classmates talking about the new transfer student and is highly interested when they mention the new student might be a member of Border.

A commotion is heard on the street in Mikado City, where a young boy, Yūma Kuga, has just been hit by a car. The boy is completely unharmed; however, to the amazement of all the people surrounding him. When questioned about his address, Replica, a small black creature, appears from inside his collar and whispers the answer into his ear. Afterward, Yūma walks down the street, talking to Replica. Replica scolds Yūma for not being careful, and Yūma asks Replica if he can use his Trigger. Replica replies it is up to him and reminds him he is late.

At school, Yūma looks inside a class, where students are taking turns reading. He is surprised that they all dress the same, questioning if it's fashion, but Replica explains it's a way to identify the students of the institution. The class' teacher goes outside and asks Yūma where is he from, and he's then taken to class 3-1. There, he introduces himself, and one of the bullies points out that he's wearing a ring. The school principal, Moribayashi, tries to take it for him, explaining that wearing accessories is against school regulations. Surprised by that, Yūma apologizes and leaves, but Moribayashi tries to stop him. Osamu defends Yūma, saying he must have a good reason for not wanting to take it off. Moribayashi then asks him the reason why, and Yūma explains the ring was a memento from his parents, and one of the bullies says so is the manga that was confiscated from him, causing Moribayashi to tell him to shut up. After a chilling stare from Yūma, the Moribayashi commovedly allows him to keep the ring, and calls their homeroom teacher, Mizunuma, to his room. Mizunuma tells Yūma to sit next to Osamu, and asks Osamu to take care of him.

Other students begin to question Yūma about his hair, while Osamu muses on his suspicions about Yūma being a part of Border, but figures he was wrong. The bullies from earlier throw crumpled paper balls at the back of Yūma's head, claiming it is a normal Japanese greeting. Yūma, seeing though his lies, makes a more crumpled paper and flicks it into the ringleader's forehead, knocking him over. Yūma claims he is returning the greeting, with Osamu is amazed by Yūma's fighting ability. Mizunuma returns and resumes classes before the bullies can retaliate. Osamu decides to keep an eye on Yūma and asks if they can walk home together. He warns Yūma about embarrassing the bullies and predicts they will retaliate.

Just then, the bullies show up and demand that Yūma comes with them. Yūma readily agrees, not realizing their motives, and starts to follow them. They tell Osamu to leave, but he grabs one by the shoulder and demands they let Yūma go. In an abandoned lot, Osamu is punched several times by the ringleader and challenges them to fight him one-on-one. Osamu warns them about being in a Forbidden Zone and that a Neighbor could attack at any time. The ringleader ignores Osamu, saying he doesn't care about Border, and continues to hurt Osamu. Yūma doesn't make any motion helps him, coldly refusing to help when questioned, as it was Osamu's fault for inserting himself into the situation. The ringleader turns on Yūma, who easily blocks his attack and knocks him to the ground by breaking his leg. Just as the rest group lunges to attack Yūma in retaliation, warning sirens begin to sound, and a gate appears above their heads, with a Neighbor coming out of it. The bullies attempt to flee, but the ringleader is picked up by the large Neighbor that steps out of the gate. As he is dangling in the Neighbor's mouth, Yūma calmly suggests that they leave. Osamu; however, says he has to save them. Yūma says they got what they deserve and asks why Osamu wants to save them, but Osamu declares it's just because it's the right thing to do.

Osamu reveals he's a Border agent, activating his Trigger, Raygust, and his clothes transform into a white outfit. He jumps up and strikes the Bamster, freeing the bullies. However, he is not strong enough to pierce the Bamster's skin, and is thrown away. Yūma again asks Replica if he can use his Trigger, and Replica again states it is Yūma's decision. Yūma activates his Trigger, and his clothes transform into a black bodysuit, to which Replica fuses itself, as Yūma leaps through the air. He easily destroys the Bamster, to the amazement of Osamu. After they both revert back to their school uniforms, Osamu questions Yūma about his Trigger and asks if he is affiliated with Border. Yūma says he isn't a Border agent. Osamu is confused, then, why Yūma has a Trigger. Yūma explains it was his given to him by his father, and he was told by his father to travel to Japan in the event of his death to find his friend who works at Border. Yūma explains his father had nothing to do with Border, either. Osamu is even more confused, since only Border agents have access to Triggers. Yūma says that rule only applies to "the world on this side". He smiles as he explains that he came from across the gate and is what is called a Neighbor, ending the chapter.

Characters in order of appearance[]

Characters in italic are only seen briefly and have yet to make a proper appearance.

Triggers in Order of Appearance[]


  • On page 18, one of the bullies is reading Super Dog Rilienthal, The Author's first serial on Weekly Shonen Jump.


Introduction Arc
Chapters 12345678910111213141516
Volumes 12
Episodes 12345678