Osamu Mikumo 4

Short summary
Osamu accepts Kazama's challenge for a Mock Battle and learns that Jin gave up his Black Trigger in order for Yūma could be an official agent.

Long summary
During Border's Enlistment Day, Kazama challenges Osamu for a Mock Battle, which shocks Yūma and the others in the Training Hall. Feeling concerned over this, Arashiyama asks Kazama if this is an order from Commander Kido. But Kazama corrects him, saying that it shouldn't be a problem since Osamu is an official agent and that he simply wanted to test his worth. Both Arashiyama and Karasuma encourage Osamu to decline. But since he resolves to become stronger and go on away mission, he accepts. Tokieda moves all the trainees out of the room, but Yūma asks to stay. Karasuma tells Osamu that he won't be able to win as he is now, and Osamu says he knows. With an impassive look, Karasuma simply tells Osamu to not strain himself.

Osamu and Kazama enter the Training Room and prepare as the fight begins. When Osamu notices that Kazama is using Scorpion, he creates Asteroid in order to fight from a distance. But then Kazama disappears and attacks him from the side. Karasuma explains to Yūma that he is using Chameleon, and Kikuchihara remarks that since Trion doesn't run out inside the training rooms, Chameleon can be used limitlessly. As Osamu loses over and over, he realizes that when using Chameleon, Kazama can't use any other Triggers. He fires Asteroid around the room, trying to catch Kazama off guard, but Kazama appears and says he is used to this strategy, and once again defeats Osamu.

Kitora asks Karasuma to stop them, since there is no way Osamu can win. Yūma says Osamu probably knows he can't win but is instead gaining experience for the future. Kitora says that if he doesn't fight to win, he won't gain anything from the experience. Karasuma admits she makes a good point, but says it is up to Osamu and Kazama to decide when to finish. Just then, Kazama puts away his Triggers, having won over 20 times. Kazama then admits to himself that he expected more from Osamu. He then says that he doesn't understand why Jin would give up his Black Trigger which shocks Osamu for he didn't know. Kazama explains that Jin had done so in order for Yūma to be enlisted as Border's agent. Understanding that Jin gave up the Black Trigger made by his mentor, Osamu asks Kazama for one more fight.

Characters in order of appearance

 * Yūma Kuga
 * Ai Kitora
 * Jun Arashiyama
 * Sōya Kazama
 * Osamu Mikumo
 * Kyōsuke Karasuma
 * Yūichi Jin (flashback)
 * Mitsuru Tokieda
 * Shirō Kikuchihara
 * Ryō Utagawa
 * Yōsuke Yoneya (flashback)
 * Shūji Miwa (flashback)
 * Takumi Rindō (flashback)