Kō Murakami/Plot

Background
About 2 years before the year in which Yūma enlisted into Border, Murakami joined Border. Murakami was mentored by Arafune, and the former found himself easily grasping the concepts of battle. 8 months prior to Kuruma Unit's Rank Battle against Nasu Unit and Mikumo Unit, Arafune quit being an Attacker. This upset Murakami, as he believed that his mastery had discouraged Arafune. Arafune assured him that that wasn't the case, though the rumour of it being true remains.

Large-Scale Invasion Arc
He operates alongside Kuruma Unit, which encounters a Rabbit. When his unit goes to join the B-Rank union, he is forced to take care of them himself. He is disadvantaged, but is prepared to put up a fight, when he is saved by Tachikawa.

B-Rank Rank Battles Arc
In round 1, his team faces off against Suwa Unit, where he is defeated. In round 2, his team goes against Nasu Unit where they win the Rank Battle.

He appears in the Rank Battle hall following Mikumo Unit's round 2 battle. Midorikawa introduces him as the reason Arafune quit being an Attacker. Murakami, seeking to fight a Grasshopper user, asks Midorikawa to have a solo Rank Battle with him. Midorikawa refuses, so Yūma volunteers instead. Though Yūma is warned that fighting Murakami would put him at a disadvantage later on, Yūma insists on fighting him. Murakami gives two conditions for the Rank Battle: it will be a 10-match battle, and there will be a 10-minute intermission between the 5th and 6th matches. Yūma accepts. In the first 5 matches, Yūma has a victory (4-1). However, Murakami goes to sleep during the interval. The following matches are easy wins for Murakami, giving him the overall victory (6-4). This makes Murakami the first person to ever beat Yūma. He is revealed to have a Side Effect of enhancing his memory in his sleep.

During the Round 3 battle, he is teleported on the opposite side of his fellow members' location. He is on the side with Yūma, Kumagai, and Hiura. He engages in a fight with Kumagai, and at one point, they make a provisional alliance to try to take down Yūma. However, this is in vain as they go back to fighting each other, with Murakami getting the victory. He is then approached by Yūma, who has taken out Hiura, and they begin their duel. Yūma uses his Grasshopper to try and outmaneuver Murakami, but it is useless and Murakami holds the advantage. However, Yūma then has Murakami step on a Grasshopper, flinging him into the river. Inside the river, Yūma uses his superior agility to get behind Murakami and stab him, defeating him. Following the Round 3 battle, Murakami has another Rank Battle with Yūma, where he triumphs. Murakami then introduces Yūma to Kageura, the captain of one of Mikumo Unit's upcoming opponents. Moments before, Kageura had beheaded two trainees (in their trion bodies) for criticizing him. Murakami assures them that Kageura wouldn't attack their real bodies, and explains that Kageura's Side Effect allowed him to read their minds. Yūma picks this up as a lie. After Kageura leaves, Murakami reveals Kageura's true Side Effect: feeling emotions aimed at him. Murakami notes that Yūma and Kageura would work together as they possess a similar air.

When the Galopoula Invasion takes place, Murakami is stationed to guard the Expedition Ship, alongside Tachikawa, Kazama, and Konami. When Gatlin and Ratarikov attack, he uses Raygust to deflect Gatlin's high-powered shots, though he does get his arm cut off by a Dog. He is successful in his mission, in the end.