|“||If you send another assassin, next time, it won't only be Arashiyama Unit. You'll be facing me, Kido Faction.||”|
–Shinoda threatening Kido about capturing Yūma, 
Masafumi is a tall middle-aged man. He has chin-length black hair and thin black eyes. In the anime, his hair has a purple tint. He also has tear-throughs around his eyes, giving him an older appearance. Being a high-ranking member of Border, he usually wears a suit, a dark greyish blue one with a black suit with a double white stripe.
In his trion body, he wears a black trenchcoat similar to Tachikawa's, albeit without the stripes, and black pants over black boots.
Masafumi is a person who cares first for people's safety. He will do anything to protect innocent people, but unlike most people at Border, he doesn't hate Neighbors. As such, he was against killing Yūgo's son to take his Ring from him, which he considered theft. Kido sees him as a mischievous brat, referring to him as such when he jumped from wall to wall to get to the training room.
- He likes training, dashimaki tamago (Japanese style omelette), shōyu ramen, and motorbikes.
- Other reasons for his nickname "Mischievous Brat" include chopping Kido's car in half while training, trying to run on the water of a river, which alerted the police, leaving a building from a window on the second floor and coming back in through one on the third.[BBF Q101]
- His surname comes from Ruka and Yōtarō Shinoda from the Talented Elite Jin one-shot.