Ken Katagiri is a former student of Suzuran All-Boys High School who later becomes associated with the yakuza before leaving that life behind. His background is marked by hardship, as he was severely bullied during middle school. He was forced to participate in so-called razor blade matches, where the loser would have his head shaved, an experience that gave rise to his nickname. Seeking to escape his past and start a new life, he decided to enroll at Suzuran, a school infamous for its delinquent students.

Upon arriving at Suzuran, Ken initially doubted his decision. However, his path changed on the day of the entrance ceremony when he met a student named Muramasa. He soon became embroiled in a fight with a student named Dejima and his gang. After rallying allies and landing a decisive punch that knocked out Dejima, Ken gained fame among the first-year students. This victory led to the formation of the Muramasa Ken Faction, a powerful alliance that included not only his own followers but also Dejima and his gang.

Ken's time at Suzuran was defined by his ambition and his willingness to face conflict. When he witnessed a student from the rival Tsuda Faction stealing money from children, he confronted the culprit despite being outmatched and losing the initial fight. This act of defiance led to a direct challenge from the leader of the Tsuda Faction, who offered Ken a choice: apologize, pay a fine, and join them, or face a war. Ken chose war. The conflict lasted about a month and concluded with Ken personally defeating his original antagonist in a rematch.

His ascent continued into his sophomore year, where he successfully recruited most of the promising new freshmen, growing his faction to around forty members. The only major obstacle preventing him from ruling Suzuran was the powerful Kotetsu Faction. However, before their inevitable confrontation could occur, his partner Muramasa was forced to drop out of school due to a family illness. Shortly after, Ken himself was expelled for nearly killing a man who was harassing some girls, abruptly ending his high school career before he could achieve his goal of becoming the school's ruler.

After graduating, Ken Katagiri did not find significant success. He became a mid-level yakuza, but his life took a new direction when he decided to mentor Genji, the son of a powerful yakuza boss. Ken lives vicariously through Genji, using his experience to teach the young man the ways of diplomacy and strategy. His primary motivation is to guide Genji to achieve what he never could as a student: to become the ruler of Suzuran. Following the events of his time as a yakuza, he left that world and found work as a salesman at a car dealership.

Ken has several key relationships that define his character. His bond with Muramasa was a powerful partnership that formed the core of their faction. His role as a mentor to Genji is central to his later actions, as he invests his hopes and knowledge in the younger man. His past also includes a rejection from the Ryuseikai yakuza syndicate, which led him to join a rival gang instead.

In terms of development, Ken transforms from a bullied middle school victim into a confident and powerful figure at Suzuran. His expulsion prevents him from reaching his full potential as a ruler, leading to a period as a disillusioned yakuza. He ultimately finds a new purpose not in direct combat, but in guiding a successor, and eventually leaves the criminal underworld entirely for a legitimate job. Among his notable abilities, Ken is a capable and determined fighter, with a record of significant victories during his school days. However, his most defining skill is arguably his diplomatic sense, which he hones after his school years and uses to mentor Genji in navigating conflicts without solely relying on violence.