TV-Series
Description
Jun Arashiyama captains Border's A-rank #5 Arashiyama Squad. He ranks as the No. 2 All-Rounder and is one of twelve candidates eligible to inherit the Fūjin Black Trigger.

He is a tall young man with medium-length, feathered black hair (appearing brown-tinted in the anime) and green eyes. His standard Border uniform features black leggings and a distinctive red, high-collared athletic jacket bearing the A-rank emblem patch on the right shoulder; long black stripes appear down each sleeve when in trigger mode.

Arashiyama displays a carefree, playful attitude, extending even towards Neighbors without inherent dislike. He prioritizes protecting civilians and colleagues, demonstrated when he defended Osamu Mikumo for violating Border rules to prevent casualties, praising his quick thinking. Strong protective instincts towards family were evident when he immediately embraced his younger siblings upon confirming their safety during an attack. His commitment was further reflected in a public interview where, after ensuring his siblings' security, he pledged to fight unreservedly for the safety of all families.

As squad leader, he oversees unit activities including public relations duties, representing Border in media appearances, and managing orientation for new C-class trainees. The squad's emblem consists of five black pentagons arranged in a star formation around a white center, each containing a smaller star. Former member Kuniharu Kakizaki departed over feelings of inadequacy when the squad was designated for PR work.

Significant operations include responding to the initial neighbor attack at Osamu's school and collaborating with Jin to prevent the forced seizure of Yūma Kuga's Black Trigger. His squad, with Yūma's assistance, became the first unit to eliminate a "Rabbit" trion soldier during the Large-Scale Invasion. They received an Outstanding Service Award (800,000 yen and 800 points) for defeating trion soldiers in the emergence zone and supporting Konami in the Southwest district.

He actively mentors lower-ranked agents, agreeing to train Osamu Mikumo in combat fundamentals despite initial reservations. Concerned over Osamu's morale following a defeat, he facilitated further training sessions conducted by squadmate Ai Kitora in his absence.

Personal notes include his pet dog Koro. He favors his younger siblings, dogs, and seafood. His surname "Arashiyama" translates to "storm mountain," sharing its name with a Kyoto district and mountain, while "Jun" means "Associate."