Ibuki Satoru is the deceased brother of Ibuki Kengo.
He looks similar to Kohinata MInoru and it is noted in the manga.
Mutou and Minari were Satoru's friends.
Ibuki was his very close brother.
In the manga it states that Mutou Ryuuji had never defeated him showing that was very strong.
In Middle School, Satoru was a member of the Soccer Club. As of meeting and fighting Mutou for the first time, Satoru claims that he's been doing Karate for only four months, surprising Mutou.
Mutou and Minami were participating in a tournament in the Kaburagi-ryu Kawasaki Main Dojo. Mutou couldn't advance to the next round because of a default loss. Mutou's hope was that he could advance so he could fight Minami. However it was Satoru who defeated Minami at the tournament.
After the tournament, Mutou challenged Satoru for a fight with the reasoning that he was the one supposed to beat Minani, not Satoru. Satoru faltered at first. After ten minutes, Mutou is shown soaked in blood and still trying to continue the fight even though he didn't even hit Satoru once.
When Satoru is 18 years old and a Kaburago-ryu National Middle Weight Champion, he is invited to participate in the K.O.S as a minor opener.
In K.O.S, Satoru fights Samart Sirinto, a thai welter weight. When the second round of Satoru's fight is over, Satoru is shown soaked in blood while Samart has barely broken a sweat
In the third round, Satoru attempts an uppercut but Samart responds with a knee kick with which Satoru goes down and loses the fight.
Satoru is sent to the Municipal General Hospital and is diagnosed with cerebral arteriovenous malformation, a congenital brain disorder. It's said that if Satoru had led a normal life, there wouldn't be any problem at all, but if he receives a strong concussion to the brain, the blood vessels in the affected area fail, and a hemorrhage into the brain occurs, leading to death.
Severals days afters being hospitalized, Satoru dies.
After his death, the K.O.S claimed that because Satoru suffered from AVM (arteriovenous malformation) they'd need a throughout examination so they could've prevented him from fighting by detecting his condition. Mifuyu, however, didn't believe K.O.S and she blames Izumi even now for his death.
The fact that Satoru died or the cause of his death were never made public due to Izumi's influence.