|First Lieutenant Tsurumi will scold me!
This article is outdated, poorly written or lacks important information. It should be reworked!
Like his brother, Nikaidou Kouhei has a well accented face with a thin, pointed nose. He has completely black irises, and his hair is black and cut very short, with a straight hairline. He is seen wearing the uniform of his ward.
Nikaidou is missing both of his ears; one was ripped off by a bear and one was cut off by First Lieutenant Tsurumi. He would wear his cut off ear on a string around his neck, but later on Edogai made him a headpiece out of human skin which the ear was sown onto where it goes over his chin. The headpiece covers most of his head apart from his face, with holes on the sides where his ears used to be, and a pair of nipples at the top.
After having his his leg cut off by Hijikata, Nikaidou receives a prosthetic leg from Arisaka which also doubles as a firearm. Nikaidou later loses his right hand in a battle with Sugimoto, so Tsurumi asks Arisaka to make him a prosthetic one, which has a chopstick compartment in one of the fingers.
Nikaidou appears mentally unstable, as he often ignores orders and seems to enjoy inflicting pain on others, which was shared with his twin brother, Youhei. After the death of Youhei, Nikaidou became obsessed with getting revenge against Sugimoto, often disregarding anything else when he finds himself face-to-face with him. His mental health also apparently deteriorated even further, as he refers to his lost body parts (leg, ears, etc.) as Youhei's instead. When told that Sugimoto had "died", Nikaidou lost his motivation and became a shell of his former self, refusing to move from his bed or eating his food. He seems to have become addicted to morphine after his many severe injuries, as he would steal entire bottles of it and just the mere mention of it was enough to get his full attention when everything else had failed.
- Type 26 Revolver
- Prosthetic leg: Not just any prosthetic leg, but a leg that can hold up to three shotgun shells and is capable of close combat for a surprise attack.
- Prosthetic hand: Kouhei was given a prosthetic hand in addition to his prosthetic leg after it was blown off by Sugimoto during the assault on the Abashiri Prison. Hidden in one of its fingers is a compartment to hold chopsticks. Kouhei was initially excited to be given another "special" prosthetic but was disappointed in its mundane usage, ignoring it and going back to his depressed state at the time.
- Nikaidou likes Mandarin oranges.
- In 2018 Golden Kamuy All-Stars popularity poll Nikaidou ranked 22nd, gaining 2 068 votes. 
- Nikaidou, Sugimoto and Tanigaki are the same age. 
|7th Division Members||Hajime Tsukishima • Kazuo Maeyama † • Kennosuke Mishima † • Kouhei Nikaidou † • Mokutarou Kikuta † • Otonoshin Koito • Tokishige Usami † • Tokushirou Tsurumi • Youhei Nikaidou †|
|Deserters||Fumio Okada † • Genjirou Tanigaki • Houzou Tamai † • Hyakunosuke Ogata • Ikutarou Komiya * • Naoaki Noma † • Rikimatsu Ariko|
|Allies||Heiji Koito • Hidenobu Okuda • Narizou Arisaka • Teruchika Yodogawa • Yasaku Edogai †|
|Associates||Kouji Wada † • Koujirou Hanazawa † • Yuusaku Hanazawa †|