First Manga Appearance: Chapter 79
Name Meaning: Tsumoi=intention; plan, Katsu=victory; cutlet, Yukie=going to
Nicknames: Big Ka; Medusa
Gangs: K. T. Butai; Oni-baku Gumi
Rival: Tamura Akimitsu
Homeroom Class: 1-F
Current School: Tsujido High School
Previous Schools: Ryou Junior High School
Transportation: Kawasaki Zephyr
Notable Features: Leader of the K. T. Butai; scar above left eye (self-inflicted); scar on left side of abdomen (required fourteen stitches); hot-tempered
Nicknamed "Medusa" when Eikichi was in 2nd year of junior high because whoever looked at him would get involved in a fight. He challenged Eikichi to a fight on 3 separate occasions & losing each time, refusing to quit. He cut himself on the forehead with a blade to leave a scar after Eikichi told him that he looked sweet & innocent. He makes a promise with Eikichi about "taking the nation". He attended Ryou Junior High where he formed the K. T. Butai, consisting of Yasuo, Saegusa, Kitamura, Atsushi & numerous other students.
He arrives at Tsujido 3 days after his K. T. Butai gang & beats up some Kita High students along the way. He is surprised to find out that his K. T. Butai gang has been attacking the Oni-baku & the Kamakura Mad Dogs & gets beaten up for not disciplining his men. He & the rest of the K. T. Butai becomes the Oni-baku's backup afterwards. He settles in at Tsujido nicely & will often beat up everyone as a way of saying hello & making himself known.
He rounds up his K. T. Butai gang & provides backup during Eikichi's fight with Takezawa Akira & the Idaten gang. He later runs into some Enoshima students with Atsushi & Yasuo & meets the Kamakura Massacre Unit's Tamura Akimitsu for the 1st time & takes an instant dislike towards him. He is stopped by Kamata & Abe & Kamata punches him in the face, telling him not to get involved with the Kamakura Massacre Unit.
Despite Kamata's warning & Eikichi's orders not to cause trouble with Enoshima due to Nakajo, his temper gets the better of him & he starts attacking Enoshima students on the train ride home. He is interrupted by Kamishima Toshiki, the previous 2nd generation leader of Midnight Angel, leader of the Kamakura Massacre Unit & also an Enoshima student. He gets challenged by Kamishima to jump down onto the train tracks. He jumps back onto the platform as a train runs towards them but Kamishima stays on the tracks, showing Katsuyuki that he is on a whole different level. They both get taken away by the police.
Upon release, he gathers up his K. T. Butai gang to exact revenge on Kamishima, Tamura & declares war on the Kamakura Massacre Unit. However, only 5 of his men meet with him. He chides them for being cowards & angrily rides off to face the Kamakura Massacre Unit on his own. He fights Tamura one on one & realises how strong his opponent is. As Tamura is about to cut his face with a blade, he is saved by Eikichi. Both parties are interrupted by Midnight Angel, led by Yasha & they get restrained by the new attackers. A battle ensues & they are stopped by the police. Upon leaving, they spot an unconscious Ryuji.
He visits Ryuji in hospital & later arrives with his K. T. Butai to backup Ryuji's fight with Akutsu, Midnight Angel & the Kamakura Massacre Unit. A massive 3 way battle ensues & he gets his rematch with Tamura. They are stopped by the police & the gangs disperse. He later runs into Nakajo, along with Tsukai & Saejima, who tells them about Akutsu's true actions. He informs Ryuji of Akutsu's plans & offers to be Ryuji's backup, along with Saejima, Kamata & Tsukai.
As they wait for Akutsu & Midnight Angel at the rendezvous point, they are confronted by Kamishima & the Kamakura Massacre Unit & realised that they got set up. He sets his target on Tamura for the majority of the fight & as both sides begin to tire out, Akutsu & Midnight Angel begin their ambush. The police arrive & he is arrested, but not before informing Eikichi of Ryuji's location inside the cabin with Akutsu. He later stays in hospital with Ryuji & Nagisa, despite wanting to run off with Eikichi & help him fight Akutsu.
Sometime after the Midnight Angel arc, his bike gets stolen by Saejima, who sells it to Makoto. Blaming Enoshima for the theft, he sets out to beat them up, causing Eikichi & the rest of the Oni-baku Gumi to follow him, including Makoto (who has modified the bike in an attempt to disguise it). They are stopped by Nakajo, who reveals to Katsuyuki & a petrified Makoto that the bike Makoto is riding is the missing bike. After he gets punched by Eikichi for acting recklessly, he goes out looking for fights to calm his anger.
When the Yokohama Calvary attacks Shonan, he sets out on his own to find the 2 leaders but without luck. He runs into Tamura & challenges him to a rematch. They appear to be evenly matched but are interrupted by the 2 Yokohama Calvary leaders, who easily beats the both of them down. Despite being in hospital, he still fights with Tamura, especially for the affections of their nurse, Mihara Nene.
Despite being ready for discharge, he & Tamura remain in hospital to get Nene. They are interrupted by Sakaki Ashura, who has apparently defeated Eikichi. Worried, he rushes off to find Eikichi, who is nowhere to be found. He confronts Sakaki for lying & witnesses Tamura apparently getting beaten by Sakaki. However, it turns out that Eikichi is fine & that Sakaki is a fraud, just taking a beating & declares himself as the victor when his opponent leaves out of boredom. Katsuyuki accidentally stabs Sakaki in the stomach.
When Ryuji introduces his kohai, Hino Ken, to the Oni-baku, it is revealed that Katsuyuki & Ken have an intense rivalry, with a history of at least 20 fights, 6 hospitalisations & 10 arrests each. This starts an intense feud between Eikichi & Ryuji. Despite Tsukai’s best efforts settle things, Katsuyuki refuses to make amends with Ken. He fights Ken on the beach, determined to prove that Eikichi is the stronger of the Oni-baku. Both Katsuyuki & Ken is taken down by Tsukai when they refuse to listen to him. However, by this time Eikichi and Ryuji have already made up.