|“||After making sure our families are safe, we'll return to the battlefield to keep fighting. To those who have lost family members, those who still have family members, and to the family members of everyone here, As long as I have this body, I'll protect everyone with everything I've got. As long as I can make sure my family is safe, I won't hold back and fight until the very last moment.||”|
–Jun Arashiyama during an interview, in Kuniharu Kakizaki.
Arashiyama is a tall young man. He has medium length black hair, and green eyes. In the anime, his hair has a brown tint.
He is always seen wearing his Border uniform. When he is in trigger mode, like the rest of his unit, he wears black leggings and a red, high collared athletic jacket with the A-rank Border emblem patch on his right shoulder, and a long black stripe going down the middle of each sleeve.
Arashiyama is a carefree type, he also has a funny attitude and doesn't dislike Neighbors that much. When Osamu violated Border's rules, Arashiyama said that Osamu didn't do something wrong. In fact, he praised him for doing the right thing. He also cares very much for his siblings as he immediately hugged them when he discovered they were safe from the Marmod attack.
- Saho and Fuku: He cares for his siblings and spends a lot of time worrying about them, to the point of embarrassing them. He is overprotecting and overwhelming.
- Ai Kitora: As the member of the unit who took over his position as ace, it can be seen that Arashiyama respects and holds Kitora in high regard. As her leader and senior, he often advises her.
- Mitsuru Tokieda:
- Ken Satori:
- Haruka Ayatsuji:
- Yūichi Jin: Arashiyama and Jin are shown to have a very good relationship. During the events of the Black Trigger Capture Arc Arashiyama comes to help Jin, and repeatedly expresses trust in Jin when questioned by Miwa on his motives. In the Border Briefing File, the relationship between Arashiyama and Jin is labelled "Trust".
- Osamu Mikumo: Arashiyama respects and cares for Mikumo, giving him advice and support whenever he needs it.
- Yūma Kuga:
- Chika Amatori:
- Kyōsuke Karasuma:
- (To Osamu Mikumo) "Good idea! You made a great work! If you hadn't done that, there's no doubt there would be victims!" 
- (In an interview) "After making sure our families are safe, we'll return to the battlefield to keep fighting. To those who have lost family members, those who still have family members, and to the family members of everyone here, As long as I have this body, I'll protect everyone with everything I've got. As long as I can make sure my family is safe, I won't hold back and fight until the very last moment."
- "Jun" (准?) means "Associate", while "Arashiyama" (嵐山?) means "storm mountain".
- Arashiyama is the cousin of Kirie Konami from Tamakoma Branch.
- According to volume 1, he likes:
- His younger siblings