Nikaidou received a headpiece made from human skin by Yasaku Edogai that covers his head, leaving only his face exposed with holes on the side for sound to reach his ears as well as his own ear buckled on his chin. He later gets his leg cut off by Hijikata, but then gets a prosthetic leg which is also a firearm capable of shooting shotgun shells. Nikaidou then later loses a hand, which was shot off by Sugimoto.
After the death of his twin brother Youhei, Nikaidou became focused on revenge against Sugimoto. 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. Nikaidou seems to have a strong craving for morphine as just the mere mention of it was able to get his full attention.
In Meiji 38 (1905), Nikaidou took part in the Battle of Mukden during the Russo-Japanese War. When 2nd Lieutenant Tsurumi and Hajime Tsukishima were severely wounded, Nikaidou, along with several 7th Division members carried them to a frozen body of water to be carried away on sledges for treatment. They came upon Sugimoto with a dead body who offered to let them use the sledges with one of the Nikaidou twins asking if he was sure. They then brought the two injured soldiers away to have their wounds treated.
During a blizzard storm, the 7th Division took shelter in a wooden building. While Genjirou Tanigaki and Tsurumi were having a somber conversation, one of the brothers whispered something into the other brother's ear.
(from chapter 70 onwards)
in the coal mining town of Yubari, Nikaidou is staking out a fresh grave along with Tsurumi and Sergeant Tsukishima in order to catch a grave robber. As Tsurumi and Tsukishima are talking about whether or not the grave robber will come, Nikaidou holds up Youhei's ear to Tsurumi's, saying that it looks just like his, and asks him to give him his left ear. Tsurumi humors him by saying that he could have it when he dies, just then Tsukishima spots a silhouetted man in front of the grave. Nikaidou steps on a branch, which the man hears and proceeds to flee. Tsurumi tells his subordinate to chase after him, with Tsukishima telling Nikaidou not to kill him. (70)
Sometime after the chase, Nikaidou and Tsukishima are seen inside a house next to the Edogai Taxidermy store, with Nikaidou scouting and Tsukishima maintaining a rifle. Nikaidou questions if the taxidermist really has the skin, to which Tsukishima tells him that he talked to a doctor about the mining incident and that he dug up the grave to find it empty. Getting impatient, Nikaidou also asks if it would be better to just kill Edogai and search his house but Tsukishima tells him if Tsurumi really planned to kill him, he'd have done so once he answered the door. (71)
While Tsurumi is occupied with Edogai, Nikaidou manages to slip inside the Edogai house without Tsukishima noticing, and holds Youhei's ear up to Edogai's mother's ear, saying that her ear won't work. He then drops the ear into her clothings and as Nikaidou is attempting to retrieve it, Edogai comes into the room and finds him and his mother in an awkward position. He is able to obtain his brother's ear and move away to allow Edogai to let go of his past and shoots his mother's corpse. Afterwards, Nikaidou is shown banging a human drum with human bones to commemorate Edogai's recruitment into the 7th division. Sometime during his visit in the Edogai store, Edogai gave him a headpiece with his ear sewn on it.
Nikaidou returns to Yubari along with several 7th Division soldiers in order to erase the evidence left behind by Edogai and throws a molotov cocktail into the Edogai store to burn it down as he whispers to his ear that they've got to erase everything.
As they burned the Edogai store, Nikaidou ordered his fellow soldiers not to kill Sugimoto as he wishes to deal with him himself. When Ogata appears on the second floor, shooting at them, Nikaidou and the other soldiers rushed to the walls of the store to hide from his attacks. However, Hijikata began firing at them, knocking his cap off, forcing them to move away from the store. Given an opportunity to enter the store, Nikaidou rushed inside only see Hijikata preparing to cut him down with his katana. He was able to react in time to tackle Hijikata and overpower him. When he heard Sugimoto shouting for Hijikata, he stopped and looked up to see him, with an eager grin on his face. He yelled out Sugimoto's name and began to move towards the other man but is stopped when Hijikata cut his right leg off. Predicting Hijikata's attack, Nikaidou rolled away to hide from Hijikata, who gave up on finding him soon afterwards. Once Sugimoto and Hijikata's group left the store, Nikaidou crawled out from the store and roared in anguish.
Nikaidou was eventually brought to a hospital in Otaru where his wounds were treated. He would often steal some morphine and had to be restrained by Tsukishima and a doctor so as not to overdose. Tsurumi then came into the room and scolded Nikaidou, which caused him to fall into a depression. Tsurumi and Tsukishima headed out to meet an acquaintance and came back just as Nikaidou tried to steal another bottle of morphine.
As Nikaidou and Tsukishima struggled over the bottle, Tsurumi called out to him and said that a guest has come to visit him. Suddenly, a strange man came in and Nikaidou and Tsukishima are confused until Tsurumi shooed him away and Narizou Arisaka came in to introduce himself. When he produced a prosthetic leg, Nikaidou showed disappointment until Arisaka revealed that it can be used as a shotgun weapon. Nikaidou is amazed by his new attachment while a doctor came in to tell them to be quiet. Tsurumi, Arisaka, Tsukishima, and the strange man congratulates Nikaidou on his new leg.
After the raid on Abashiri Prison, Nikaidou was brought to a nearby clinic on the outskirts of Abashiri to be treated for his wounds, including the loss of his right hand. Sometime afterwards, he was told by Tsurumi that Sugimoto had "died", unaware that Sugimoto was in fact still alive and currently on a mission with Tanigaki, Tsukishima, and Koito. With the objective of his vengeance gone, Nikaidou felt he no longer has a purpose in life and refused to move from his bed or eat his food.
Nikaidou was then visited by Tsurumi who had heard of his current state from Usami and tried to get him to eat his food by rewarding him with some morphine. They are then visited by Arisaka who had crafted a prosthetic hand for Nikaidou, which piqued Nikaidou's curiosity. However, after finding out that the hand's special trick turned out to be a chopstick holder, Nikaidou was not amused and returned back under his covers.
As Nikaidou recuperated from his wounds, he listened to Tsurumi talk about Kiroranke's past and his involvement with the assassination of Emperor Alexander II of Russia.
Abilities and Equipments Edit
Prosthetic leg: Not just any prosthetic leg, but a leg that can hold up to two shotgun shells and is capable of close combat for a surprise attack.
Nikaidou likes Mandarin oranges.