Osamu Mikumo's Ability

Short Summary
''Despite Yūma's warning that he will die if he attacks such powerful Trion soldiers, Osamu rushes in to save his fellow students from the Marmods. After ensuring most students are safe, he is quickly outmatched, but is rescued by Yūma, who uses Osamu's Trigger to defeat the Marmods. Replica, introducing himself to Osamu, gives him an explanation about Trion and Triggers. Afterward, Yūma lies to everyone, insisting Osamu saved him. Arashiyama Unit then arrives on the scene and is surprised to learn that the Marmods were defeated by a C-Rank trainee.''

Long Summary
A gate opens above Third Mikado City Middle School, which lies outside the Forbidden Zone, and combat type Trion Soldiers - Marmods begin to attack. As the students and teachers attempt to rush to safety, Osamu heads out to face the threat. Yūma warns Osamu that with his limited abilities he will die if he tries to attack the Marmods and to wait for Border.

The Marmods continue to swarm the school as Yūma explains that it would take 20 Osamu's to defeat one Marmods, and 18 of them would die in the process. Osamu hesitates, but when he sees Chika he resolves to not run away. In the school, Osamu's classmates are surrounded by Marmods. They are shocked when Osamu rushes in to rescue them.

For a moment Osamu believes he has the upper hand battling in a confined space, but a large Marmod slices off his arm. Yūma begins to worry about Osamu's Trion body and debates on helping him out. Once again, Replica reminds Yūma it is his decision to fight or not and also reminds him of Osamu's warning to not let anyone know he is a Neighbor. In the city, three Border agents make their way to the school. Back in the school, Osamu's Trion form is completely destroyed by the Marmod, leaving him helpless in his physical body. Yūma activates a shield to rescue Osamu and borrows Osamu's Trigger in order to fight without anyone finding out it was him. The Trigger scans Yūma's body and creates a Trion body in a Border uniform and begins to fight, despite Osamu's repeated objections. The Marmod's incredibly strong blades begin to wear on the Trigger's blade, which Osamu reveals is only for training. Yūma repeats Osamu's words from earlier about the advantage of fighting in a confined space and quickly destroys the remaining two Marmods.

Osamu is confused about how Yūma was able to defeat the Marmods with his training Trigger. Replica appears in his floating-head form and introduces himself as Yūma's chaperone as well as a multipurpose Trion soldier. Replica explains that Trion comes from the Trion gland, and value differences exist in their function and strength depending on the user. Thus the difference in their ability to use the training Trigger comes from the difference in Trion between Yūma and Osamu. While the students look on in surprise, Osamu appears from the rubble pretending to rescue Yūma. He begins to feel guilty about taking the credit, but Yūma jumps in and further embellishes the story. Osamu is not too pleased to be called a hero.

The Arashiyama Unit then appears at the school and ask who was responsible for defeating the Marmods. Yūma encourages Osamu to step forward and be praised, but Osamu admits he is still a trainee and is not permitted to use his Trigger off the base. He steps forward and claims responsibility to the surprise of the Border agents. Jun Arashiyama thanks Osamu, since his younger brother and sister actually attend the same school. As Arashiyama embarrasses his siblings, Osamu explains that the Arashiyama squad is incredibly popular and often shows up on TV. Confused and perhaps suspicious of why Osamu continues to deny his skill, Ai Kitora jumps forward and proves she could easily destroy the Marmods. She further demands that Osamu is punished for his unauthorized use of his Trigger outside the base.

Characters in order of appearance
Characters in italic are only seen briefly and have yet to make a proper appearance.
 * Osamu Mikumo
 * Yūma Kuga
 * Chika Amatori
 * Ichinose
 * Futatsugi
 * Miyoshi
 * Yotsuya
 * Jun Arashiyama (Debut)
 * Ai Kitora (Debut)
 * Mitsuru Tokieda (Debut)
 * Haruka Ayatsuji (Voice only)
 * Replica
 * Saho Arashiyama (Debut)
 * Fuku Arashiyama (Debut)

Adapted From

 * Chapter 4
 * Chapter 5
 * Chapter 6 (page 1-10)

Differences Between the Anime and Manga

 * In the manga, Arashiyama Unit isn't seen until they arrive at the school, while in the anime, they're seen on their way to the school.