|“||The world is a harsher place than what a child conceives.||”|
Masamune Kido (城戸 正宗 Kido Masamune?) is a character in the manga and anime series World Trigger. He is Border's highest person in charge. Due to his actions, he is the main antagonist of the Black Trigger Retrieval Arc.
In the early days of Border, he had longer, with most of his fringe slicked back, and a short strand of hair framing each side of his face. He also had no scar on his face, which could mean he received the wound during the tragedy before Border went public. In the portrait, he left in his old room in the old HQ (currently Tamakoma Branch), he wore a cardigan over a dress shirt, along with dress pants and dark loafers. He was also seen smiling.
Kido is a serious and strict person, and dislikes anyone who breaks the rules of Border, like Osamu did. However, he was shown to be somewhat forgiving to Osamu, encouraging him to achieve his goal. Like most of his faction, he hates Neighbors and considers them enemies of the Humans. When he thinks necessary, he is willing to take extreme ways to accomplish his goals.
Kido and Yūma's relationship starts off the worst when Kido finds out Yūma is both a Neighbor and the bearer of a Black Trigger. Despite him being the son of Yūgo Kuga, or due to there being no proof of it, Kido orders Jin to eliminate Yūma, but Jin refuses, with his branch leader, Rindō ordering him to capture Yūma any way he wants. Kido starts becoming more determined to get the Black Trigger, and orders several A-rank units to go after Yūma. After being stopped by Jin, and having to accept Yūma as a member of Border, he becomes more accepting of him, promising that Yūma would not be hurt as long as he followed Border's regulations. He even allowed Yūma to use his Black Trigger during the Second Large-Scale Invasion under the condition that he didn't leave the Danger Zone.
- (About Osamu Mikumo) "People who don't abide by Borders's rules are not needed in my organization." 
- (To Masafumi Shinoda and Takumi Rindō) "That mischievous brat..." 
- (About Shinoda) "That mischievous brat..." 
- (To Osamu) "Work hard to reach your goals." 
- He likes his family, old movies, and black coffee.