Nikaido (ニカイドウ) is Kaiman's companion, and they both hunt Magic Users. She is the owner of a restaurant called the Hungry Bug in the Hole. There she serves primarily gyozas with a few slices of shiso, which Kaiman adores. She is secretly a Magic User.
Nikaido is a young, attractive woman with long blond hair, blue eyes, an athletic body build, with a curvy figure (shown mostly after her Devil training). At the beginning of the series, her clothes consisted of dark baggy pants and a black jacket with a Chinese design. About midway in the series, she wears green overalls with combat boots and leather gloves.
During the time as En's partner, her clothes changed to a red jumpsuit with black boots and gloves. While captive and sick in En's Mansion, her outfit consisted of a black jacket and black panties. Most of her body was covered in bandages due to her body's resistance to healing properly.
During devil training, she used a heavy, impractical black armor to make her body appear more like a Devil. After she began to change in body type, she started wearing a set of shoulder and leg guards, a hoodie, and an apron with nothing to cover her under the waist. This was mostly due to her "devil side," preferring practical clothing, despite appearance. After regaining consciousness, she changed to a more modest set of green overalls over a white tank top.
Nikaido has an easy-going and friendly attitude, though she keeps many of her worries and anxieties to herself. She is confident in her physical abilities and isn't easily frightened.
Born in the Magic-User Realm, Nikaido became an orphan when she was still a baby. Raised by an elderly couple, she lived a happy life with other adopted orphans. Her older sister Yakumo and brother Kawajiri, played with her and trained her sister in martial arts and acrobatics. Making her extremely skilled in combat and stronger beyond an average sorcerer (able to defeat even adults easily).
By the time her brother took the Devil exam, Nikaido had produced her first traces of smoke. After a while, she was able to create a tiny cube of black smoke (thinking it was candy, Kawajiri told her not to put it in her mouth). She practiced until she was able to produce a black box, big enough for her to come in, accidentally traveling back in time, and running into a young Kawajiri and their adoptive parents. Not knowing who she was, they headed home to were Nikaido asked where Yakumo was, not knowing what she was talking about. The little girl ran desperately to the river where she found a tombstone near where Yakumo was supposed to be found by her parents. Knowing that her interference in the past killed her sister, Nikaido unsuccessfully tried over and over to rewrite the past. Drifting every person she knew away from each other until she was found in the streets by Kawajiri (Now an orphan raised in the Devil's church almost turned into a full Devil). She saved him from a group of Magic Users who capture him for the Blue Night to make him use his magic and lose his Devil position or become the partner of one of them. The little Nikaido defeated all of them and let Kawajiri escape.
Days later, now a full Devil, "Asu" found and helped her with the firm resolution to go and live in Hole, where she will never need to use her magic anymore.
While living in Hole, Nikaido took to selling gyoza but was unable to afford her own place. One day, she found a shop that was being assaulted by the victims of various practicing Magic Users. They demanded that the owner, Syueron, close the shop as Magic Users frequented the location after practicing on the people of Hole. Nikaido, being unaware of their reasons, confronts, and drives off the angry victims. Afterward, Syueron recruits her to be the shop's bodyguard and to sell her gyoza with him. One morning, they return to find that the shop had been broken into and trashed. This prompts Syueron to go with Mr. Moroku, a Devil and old acquaintance of his, to open a new shop in the Magic User's realm. He leaves the shop to Nikaido, who rebuilds it into The Hungry Bug.
Nikaido, in the past, was part of a volunteer group that recovered the bodies of the people killed around Hole. While in a dark corridor, she finds a large decapitated body and proceeds to put it into a body bag before reporting the corpse to Dr. Vaux. Later, when they arrive to take the body to the Hospital, they find it upright and walking towards them. Nikaido removes the bag and finds a blood-soaked man with a reptile head. They take care of him, and Nikaido begins to call the man Kaiman, the two quickly become close friends. Kaiman becomes a huge fan of Nikaido's gyoza, and she promises to help them look for who was responsible for transforming his head. Together, they hunt down the sorcerers who come to the hole looking for practice, typically killing them after they answer Kaiman's question of what "the man inside his head" said.
She is one of the first characters of the manga, fighting Fujita while Kaiman "interrogates" Matsumura. She breaks the sorcerer's finger and kicks him to the ground. Fujita manages to escape through a Magic Door before Nikaido and Kaiman could get to him. Afterward, the pair decide to go back to her restaurant for food. After running an errand to get roasted pork and passing through the Hospital was Kaiman is working, she finds a young man outside of her door asking for food. She invites him in and is immediately assaulted as she discovers he is the sorcerer responsible for the recent attacks that have been partially turning people into bugs. Later, Kaiman finds her in a similar partially transformed state and rushes her to the Hospital before setting off to hunt down and kill the sorcerer. Upon his death, the transformation effects are undone, and Nikaido returns to normal.
After a trip to see the photos, Nikaido took of Kaiman's mouth (to see the man inside his mouth), they assault a Magic User with a skull mask, chopping off their fingers to stop the smoke from coming out and tearing the sorcerer's mask apart. They are shocked to discover that she is a little girl. Regardless, Kaiman sticks his jaws around her head to be interrogated. Shortly after, a Magic Door appeared in front of Nikaido and the sorcerer she let escape dragged the little Magic User through the door, leaving them alone to finally see the pictures. To Kaiman's disappointment, Nikaido just found out that he had tooth decay.
During the Night of the Living Death, she and Kaiman participated as zombie exterminators to collect enough identification plates from the corpses to exchange them for a mincer. So that Nikaido could make gyozas more efficiently, they had an encounter with Shin and Noi, En's cleaners sent to kill them. Nikaido fought against Noi, who was impressed with her fighting skills and even asked to be her friend before resuming the fight. Overpowered and severely injured, Nikaido saw Shin chop Kaiman's head off. She used her magic to open a Magic Door to escape to the Hospital, where Dr. Vaux found them and treated their injuries.
Nikaido entered into a boxing tournament against [Red Brake]] to earn enough money to pay the bills of the restaurant, Nikaido came into a boxing tournament against Red Brake, magically altered humans with super strength and durability. She endured more than anyone. But after some serious hits, she was beaten and imprisoned behind the stage to be sold as a guinea pig by the Magic User who cast the spell on Brake. Kaiman came to save her by challenging Brake, by brute force Kaiman was able to damage him but was soon overwhelmed by the boxer's superhuman strength. Nikaido woke up to see Kaiman on the screen and killed the Magic User who captures her. This dispelled the magic on Brake and revealed him to be a fragile old man. Kaiman stuck him on the wall with a single punch, and both left the Noshinto Gong. She kept all the money earned by the sorcerer she killed. Kaiman was against the idea because it was dirty money. She only replies that it was his fault because he never pays for the gyoza he eats.
During a trip on New Year's night, Vaux asked her and Kaiman to go to the house of an old friend of his. They got lost for hours in the huge Mansion, which was being warped by magic. They decided to give up and have their new year's dinner in the dining room. They were found by Prof. Kasukabe, an old scientist who researches Magic Users and the corpses of sorcerers killed by the pair. After their meeting, the Professor explained to them his research, and Nikaido chooses to go with Kaiman to the Magic Users Realm to track down the sorcerer responsible for his head. They use an artificial Magic Door that Kasukabe made using the corpses of the Magic Users.
Going to The Magic User World
In the Magic User realm, they spend a couple of days living in the apartment of a taxi driver, Magic User that Kaiman killed soon after arriving. Having a sudden spur of memory, Kaiman told Nikaido that they needed to find the man called Risu, as the only link he had with his past.
With that information and knowing she will need a huge amount of money to get the answers they needed, she went to a pawn shop to sell her unique type of smoke. After receiving a large amount of money, she killed the shop owner, destroyed the Smoke Flask, and headed to meet Asu. Once again, the Devil was happy to see her again, but could not help her because no Devil knew about a man called Risu, but got clues to find him in En's Mansion.
With his help by using his Magic Door, she was able to sneak inside the Mansion, knocking and killing some goons in her way looking for the Cross-Eyes man. She was intercepted by Noi and fought once again, still far beyond her powers, Nikaido had to incapacitate the cleaner by cutting her eye so she would be able to escape and continue her search.
Searching in En's Mansion to kidnap Risu, she spots the robotic Risu through a window and leaps forth and crashing in the room at the same moment the Family Boss, En, enters. Nikaido punches En and breaks his face mask, and that unleashed his rage, releasing a tremendous amount of smoke and morphing everything into Mushrooms. Her back was also affected and morphed into a giant mushroom, desperation, and knowing nothing could be done. She escaped with no results, ending in the apartment again and asking Kaiman to cut the mushroom with one of his knives.
They had to leave the sorcerer's realm after she tried unsuccessfully to kidnap Risu. They headed to Hole using a smoke spray that Kasukabe gave to them so that Nikaido could have surgery for the mushroom in her back.
Back To Hole
Nikaido stayed in the hospital, still recovering from the surgery and cursing the fact that it is raining, wondering if there is no other choice than use her magic to help Kaiman recover his face and memories. Kaiman kicks the door and brings Nikaido's dinner, charcoal-like gyoza, with raw garnish inside. Nevertheless, she still eats them. A crazy man abducts her, and thanks to the rain, she is too weak to fight back. During the struggle between Kaiman (who came to save her), the man, and his pet monster called Jonson, Nikaido is rescued and returns to the Hospital after Kaiman killed her captor and Jonson ate his remains in the sewer.
She was part of the Hospital's baseball team called "The Worms." During the annual match between the Hospital doctors and the Heiwa Clinic doctors go against each other to see who is better (Vaux and the clinic director hate each other). After a lot of goodies and crazy things, Nikaido accidentally knocked out with a loose ball, the director, and the match was suspended for another year.
Nikaido was shocked to discover Kaiman went to the Magic User Realm without her, to prevent her from getting hurt for his fault once again, knowing him, she accepted his decision and stayed in Hole.
Back in the Sorcerers World
During the Birthday party of Dr. Vaux, where she, 13, the doctor, Prof. Kasukabe and Jonson, celebrated in the restaurant, the Professor told everyone about Nikaido's secret identity as a Magic User, everyone said to her that was ok. No one would discriminate her (only 13 was freaked out by the news) when suddenly a giant mushroom grew from her back, (En found out Nikaido's time-type magic, tranking her using the traces of his magic in Nikaido's body) Vaux and Kasukabe took off the mushroom in her back. But apparently, where a mushroom has grown, others can thanks to En's magic, the creature quickly overpowered everyone in there. Hence, Nikaido had to use her mask, the thing she vowed never to use, to empower herself and fight the creature back. With the monster destroyed, a magic door appeared and brought all of them to the Magic User world.
En imprisoned her until the Blue Night festival, where they would become partners. She remained in a cell after the contract inside her was signed to ensure her mind will be warp to obey En, in the end, Chidaruma himself crafted a special mask for her to be in total control of En. Thanks to Nikaido's old mask, the Devil found that Asu kept the secret of her existence from him.
During her time as En's partner, she was nothing more than an emotionless doll. But she retained her consciousness. Even if she was unable to express herself, she wrote a journal in case her memories would be erased due to the contract inside her. She writes stories about her childhood, family, and why she never uses her magic again.
Kaiman found her when he sneaked into the Mansion (Asu, worried about her, told Kaiman about her situation and went to rescue her) they ended fighting in a one-sided match (Nikaido, almost fully controlled tried to kill him without holding back). Both ended beneath a Devil Church. There, her contract was removed by force (Kaiman, momentary possessed by the killer intents of an old persona, stabbed her). Now with free will once again, Asu appeared to teleport both as far as he could and transformed Chota into a copy of Nikaido to fool En as long as he could.
After a warm reconciliation and promising each other to watch the other back, they stumbled into Natsuki, a Cross-Eyes girl that took Kaiman as her superior. They accompany her to her town. There they stole some clothes and headed towards Zagan, a city where Kaiman discovered the "truth" about his past. Nikaido rested in a luxury hostel with them, where they were attacked by En, now knowing about the scam of Asu, he tore Kaiman from the inside out using his Mushrooms (at the same time that Ebisu was killed by her doppelganger) dispelling the curse in his head to let Nikaido see him with his real face one more time before dying at her arms, she was once again captured by En and stayed for over a month in the Mansion, but thanks to her resistance to regrow the contract with En inside her chest, her body could not be healed even by Noi and started to rot from the inside-out.
Kawajiri found her when he came to the Mansion to rescue her. With him is a tall guy called Aikawa, who sounds and talks exactly like Kaiman. He's eager to know if he was her deceased friend. She fought him to take his mask off (Aikawa was resilient to do it simply because everything around him was not his problem) once the man shows his face to her, he escaped through her window. Kawajiri asked her if she wanted to go after him, with a sure yes they started to look for him until the Mansion fell in chaos when En was killed by the Cross-Eyes Boss. Kawajiri took Nikaido to live with him in his luxury house, where he explained to her that she no longer need to fear her magic, and must reclaim all the things she lost with her own power, helping her to improve her control over magic.
Training to master her magic
During their training (similar to his booty Devil Exam, due to the pressure in the Magic Users' body they magic become stronger and their minds more focused), Kawajiri gave her a heavy, impractical armor, twice as heavy as the ones usually used in training. Sparring with her and even buying his own severe Devil body parts from the store to make dinner so her powers would increase (to Nikaido disgust). He told her that no one knows how time travel magic works, due to the lack of historical records of Magic Users like her. She told him about a secret door to a room where they could find an old book about her magic. Disguised as gender-bent Cross-Eyes, they sneaked into the En's Mansion (now controlled by the Cross-Eyes) and found Risu and Aikawa once again. After retrieving the book and before Nikaido could talk to her former friend once again, Aikawa trusted them with Risu before he loses his senses again. They leave the Mansion with the frustrated Cross-Eyes and headed to Kawajiri's house again, where the three of them lived for a while.
Nikaido eventually perfected her control over time travel magic, creating a magic time machine box, and destroying Kawajiri's house in the process. They headed to Hole, and living in the Hungry Bug, Kawajiri accompanied her to rewrite history by saving Yakumo from drowning in the river near the house where they originally lived together. After they returned to the present, she found out that her Magic has a limit, (her magic box works like a shotgun, having cartridges heavy and hard as diamonds that disappear after she travels in time).
Later she helped Risu, to unravel the mystery between Aikawa and Kaiman. She traveled back in time two years ago to the alley where she found Kaiman. There they hid to see a Magic Door materializing and watching The Cross-Eyes Boss come from it to escape from the Magic User realm, and more precisely from Curse. The duo also noted the human and a little Jonson hiding not too far from them (the human would be in the future the one who kidnaped Nikaido using the giant cockroach to subdue Kaiman). Not much later, Curse materialized from the door lock, tearing Kai's head apart, and was almost killed by it. But not before he crushed a bottle with Ebisu's smoke, her magic, Curse magic, and the Hole influence inside his body canceled each other, rendering his body invulnerable to magic.
Consequently, imprisoning Curse inside his mouth and becoming amnesic in the process, and morphing the new head with reptilian features, during that series of events, Kaiman was born. Risu was so shocked by the revelation of his only friend in the world who killed him that Curse was triggered immediately. Nikaido, finally understanding Kaiman, headed with the disturbed Cross-Eyes to the present.
Central Department Store Story Arc
When her devil side took over her, she changed her clothes to a set of big and covered legs, shoulder guards, a hoodie, and an apron with no pants or underwear. Kawajiri and Risu were victims of her dangerously delicious gyozas (so good that can destroy your brain). The remaining gyozas were packed and sold in the central department store, where all of them got trapped thanks to the power of Devil Kai. Thanks to her transformation into a devil, she escaped from the madness inside the store, just to end up succumbing to the Devil's sudden change of humor, and went on a shopping spree in the middle of the chaos. Once she got back to her senses, she changed clothes to a more proper outfit, she looked at a shady figure with a devil tail behind her and found a disoriented Kaiman in the floor of the building.
Eager to hug and salute her lost friend, Nikaido became suspicious immediately about how it could be possible that Kaiman, a being created by a series of convenient events, exist in front of her. She hits him demanding to know who he was, with Kaiman answering only in the rude and silly way he is known for. Noticing how the spikes of his head were cut, and that this Kaiman does not remember anything after the last Day of the Living Dead, she concludes this is a "New" Kaiman. He resurrected using the head torn apart by Shin a year ago and stoled by Curse (know in her room in En's Mansion).
Still unsure about that, she tried to kill him until a Devil stopped her in the hall's roof. The Devil told her not to kill him, and they needed to find The Store's Kitchen Knife first to get out of the building. Disoriented and overwhelmed for the situation, the devil side of her took control once again and promised Kaiman to tell all the things he always wanted to know, who cursed his head, who he was, how his face actually looks like, making him confused and angry. Finding the Black House, an entity related to The Devils, Nikaido asked it to send them to Haru, the Devil that had the Knife.
The duo found the Devil, and after a brief, peaceful negotiation failed, they attacked her. They took the Kitchen Knife from her at the cost of Kaiman's life. Killed by the Devil's acid breath, Nikaido went back in time to prevent this outcome. Leaving the knife to her past self, who gave the Knife to his friend before he could banish to let the time-traveling Nikaido who stopped the previous future exist.
Devil Kai assaulted Nikaido, now ascending as a full Devil, using his powers to weaken her, stole both her time machine box and the store kitchen knife, and even with Ai/Kawa help captured and almost killed. Still, thanks to Curse Risu interference, fully mastering his new powers by chopping off the last head of Devil Kai, they were saved and headed towards the final battle against him.
Nikaido's body started to morph into a Devil, now sporting a heavy muscular build and an entirely male body, leaving just her head unchanged. The process was a disturbing scene for everyone around her.
Once Devil Kai was killed once again by En and Curse Risu, the whole place became pitch black, and acid started to flow in the floor, knowing Kaiman would not survive this, she did what she could, as Kawajiri teleported both to safety into The Black House.
Kaiman woke up alongside a completely normal-looking and naked Nikaido, as she explained what she had to do to save his life, the lizard head understood they were actually inside her Devil body. After almost drop the kitchen knife inside her, the infuriated sorceress kicked him out of her body, just in time for the final step of her transition, becoming a full Devil, with her mask now fused to her head (Kaiman was utterly freaked out by this).