The list of characters listed by group.
Yako's Detective Agency
Neuro Nōgami (脳噛 ネウロ Nōgami Neuro)
- Seiyū: Takehito Koyasu
- The title character of the series, Neuro is a demon detective from hell with a very arrogant, sadistic, and self-centered personality. He came to the Human World to look for the Ultimate Mystery, which is "the most complex, the most unfathomable, and so, the most pleasing to the palate". Upon arriving to the surface, he met Yako and forced her to become the front that Neuro needed to look for mysteries. While working on cases, Neuro usually makes use of his demonic powers and abilities to find and defeat the culprit (and sometimes to torture Yako, which he enjoys to do on a daily basis).
Yako Katsuragi (桂木 弥子 Katsuragi Yako)
- Seiyū: Kana Ueda
- Yako is a 16-year-old high school girl and the very first character introduced in the manga. She meets Neuro when he appears and desecrates her father's shrine while promising to help solve the mystery of her father's death. This meeting quickly leads to a partnership: Yako becomes Neuro's cover, pretending to be an investigator while Neuro acts as her assistant.
- Although at first it seems that Yako's only purpose is to be there as a cover, she later proves herself worthy by being able to decipher the criminal's motive by using her ability to understand human psychology, something that proves to be useful in certain cases, given how Neuro is unable to understand how humans "operate".
Shinobu Godai (吾代 忍 Godai Shinobu)
- Seiyū: Hiroyuki Yoshino (anime), Kishō Taniyama (radio drama)
- He is the jack of all trades for the detective's office and is sometimes referred to as "Neuro's second slave". Godai is quick-tempered and yells a lot, but has also been shown to be methodical, responsible, and trustworthy. During the early chapters, Godai worked for a small finance house with criminal connections. However, he was forced to work for Neuro after the latter won the bet for the office by solving their boss's death. In the manga, he was left to be until Neuro found a use for him, in which the demon then forcibly drags him back to the office, and is currently running an Information Company under Neuro's supervision.
Akane (あかねちゃん Akane-chan)
- Akane is a corpse in the wall of the office Neuro took over, who is shown only as a detachable braid of hair, which functions like a hand. Neuro offered to make Yako brush and care for her in exchange for secretarial work. Akane can be taken from the office for short periods of time and can also merge with Yako's hair to make it longer, which not only gives Akane control over Yako's natural hair, but if left merged for too long, would make Akane and Yako switch places completely. Akane later appears attached to Yako's new cell phone.
Tokyo Police Department
Eishi Sasazuka (笹塚 衛士 Sasazuka Eishi)
- Seiyū: Kōji Yusa
- Sasazuka is one of the two police officers assigned to solve the mystery of Yako's father's death. He was also a former classmate of Usui and Tsukushi in the police department. After Neuro solves the case of Yako's father's death, Sasazuka gives them access to crime scenes, arrests the culprits as Yako points them out, and deals with the aftermath. Sasazuka appears listless and disinterested at times but he has an agile mind, acts very quickly in any emergency, and is an excellent shot. He usually takes a kind and cooperative attitude toward Yako, and is protective of her because of her resemblance to his little sister, but appears to be somewhat suspicious of Neuro. Sasazuka later watches as Neuro unleashes his 777 demon weapons and learns Neuro is a demon. He and Godai share a mutual disliking but also understanding. Sasazuka has been searching his entire life for the person who killed his family, when he finds out that Sicks killed them, he goes after Sicks turning into a madman and killing everyone in his way. He's injured by X and then killed by Sicks.
Jun Ishigaki (石垣 筍 Ishigaki Jun)
- Seiyū: Kōsuke Toriumi
- Ishigaki is a young police officer. After the mystery of Yako's father's death, Ishigaki becomes Sasazuka's new partner. As a typical modern young man, Ishigaki is flippant, careless, and has low self-respect. He idolizes Sasazuka, but does not share his feelings that citizens like Neuro and Yako can interfere with police business. He is very interested in all kinds of toys and models and is shown regularly collecting them; however, they are almost always destroyed by Sasazuka, as he finds Ishigaki's habit of showing them off (as well as Ishigaki himself) annoying; this attitude is implied to be shared throughout the police department.
Naohiro Usui (笛吹 直大 Usui Naohiro)
- Seiyū: Hidenobu Kiuchi
- The boss of the Tokyo Police department. A hot-tempered but very capable man, he disapproves of incompetent people such as Sasazuka and Yako (from his point of view). He and Eishi went to the same police training school where they were rivals, with Eishi being the better one. The day Eishi's whole family was killed, Eishi had given up on being the top and gave up on their one sided rivalry. Because of this, Usui could not prove to be the better one and thus holds a slight grudge against Eishi.
- Sicks thinks of him as the sort of person who is neither "common" nor at the top, but a "middle" man who could arise when the world is in chaos and change history.
Yūya Higuchi (篚口 結也 Higuchi Yūya)
- Seiyū: Nozomu Sasaki
- A nineteen-year-old hacker/detective who works for the police. Although he is far-sighted, he only wears his glasses when using the computer, letting them rest on his forehead the rest of the time. He has a care-free personality but is highly intelligent, and seems to look up to Usui. During the HAL Arc, he was infected with the Electronic Drug to become one of HAL's guardians, although the infection was only half complete, because he was wearing polarized lenses specially made to protect himself from it. After the HAL arc, he was forced to watch shows on how to be polite drugged with the anti-virus for the Electronic Drug.
Andrew Sixson (アンドリュー・シクソン)
- A British investigator dispatched by Interpol. He was an acquaintance of Usui's, from when the latter was an exchange student in England. Sixson is capable of memorizing vast amounts of information extremely quickly, picking out a single bit of information by listening to multiple radio stations at once, or reading through a stack of papers in an instant. He is a distant relative of the New Bloodline. He was kidnapped, tortured to the point where only his head and his organs remained held up by a metal structure. He was killed by Sick's underlings and had the skin off his face peeled off so that Sicks could pose as a member of the police.
Shizuka Todoroki (等々力 志津香 Todoroki Shizuka)
- A female detective who is a new addition to Sasazuka's team, though she appeared slightly before her major debut in another case. She is a serious woman who is the opposite of Ishigaki and looks down on him; she also sees him as a rival for Sasazuka's approval, whom she has very high opinion of respect for. She was originally believed to be a replacement for Ishigaki, and constantly out did him in various police acts, a fact that more than worried him. However, during her first case in Sasazuka's team, when she questioned and insulted the criminal's motives for murder, she was promptly attacked and had to be saved by Sasazuka; it was then that Sasazuka noted to her that her seriousness was, in a way, a hindrance to her abilities as a detective, a hindrance Ishigaki is noticeably without.
Aya Asia (アヤ・エイジア Aya Eishia)
- Seiyū: Minami Takayama
- A world-class idol and the very first customer (in the manga) who comes to Neuro's office to hire the detective team to figure out who murdered her managers/friends. After the culprit is mistakenly believed to be a crazy fan of Aya, Neuro and Yako reveal (each through their own ways) that Aya was the real culprit; and although she murdered her friends in cold blood, Yako believed that she hired them as a last chance to clear her conscience.
- Aya's singing voice not only affects humans, but it also influences plants and insects as seen in her prison conversation room. She is Yako's confidant when in need of advice and counselling, as they seem to get along very well, even after her arrest, as Aya believes that Yako has somewhat liberated her a bit from her guilt.
- Her real name is Aya Aizawa.
X/Phantom Thief Sai (怪盗X/サイ Kaitou Sai)
- Seiyū: Romi Paku
- Known around the world as Phantom Thief X, in Japan his name is formed from the words 'Kaibutsu Goutou (monster robber) Xi' (the X standing for his Anonymity, and the i for 'Invisible'); this is abbreviated into the name 'Kaitou Sai', and thus X is pronounced Sai throughout both the Anime and Manga.
- X is a mysterious human with supernatural powers. He believes himself without an identity and, in a desperate attempt to find one for himself, starts taking people apart and studying their insides to find out something to which he can associate himself with. He kills people and puts them in a "red box", so that he can have a better look at their cell structure. He is intrigued by Neuro because of his demonic origins, which he believes will solve his true identity. With that reason, he chases and tries to kill Neuro to see his insides several times.
I/Ai/Imina (イミナ Imina)
- X's assistant. Formerly a government-sponsored terrorist who brought down planes, named Imina. She is the one who enforces X's "Kaitou" image and status by prompting him to take something from each place he murders in: however, X simply takes whatever is closest to him and "gives it away" to Imina, to her apparent displeasure. Depending on the day, she refers X as Master, child, friend, lover, brother, sister or others. 
- She is killed by Sicks by a bullet wound to her head.
Hayasaka Brothers (早坂 Hayasaka)
- Hisanori Hayasaka (早坂 久宜 Hayasaka Hisanori) is the older brother. He smuggled in weapons and drugs that he was supposed to be bringing in for the company he worked for, but was actually planning to kill his superior, Mochizuki, in order to take over. Neuro managed to stop him from doing so. Later, he and his brother started "Smiling Face Ltd.", a company front for smuggling drugs and weapons as well as black-market trading of organs and other illegal things. Hisanori is always seen smiling, a mask he uses to conceal his real (usually evil) intentions.
- Yukinori Hayasaka (早坂 幸宜 Hayasaka Yukinori) is the younger brother, nicknamed "Yuki". He is originally seen wearing a heavy winter coat at all times, which he uses to hide weapons. He has a great deal of loyalty towards his older brother. In his past, he and his brother lived in a very cold and poor town where everyone looked out for themselves. Their parents left them long ago so they were left to fend for themselves on the street. During that time Yukinori was buried under due to an avalanche and his brother saved his life. Hayasaka joined a criminal company and invites Yukinori to be his subordinate.
Eisuke Harukawa (春川 英輔 Harukawa Eisuke)
- A genius neurologist and computer scientist at Sakuba University. He is the creator of HAL and the Electronic (Denshi) Drug. After finding out that the Electronic Drug had been used by HAL on hundreds of people rather than his two selected test subjects, he was killed by HAL's three supercomputer guardians; his former students Tatsuo, Shiho, and Hiroto. The reason behind creating HAL was so that he could recreate a patient of his, who was slowly losing her self from a mysterious brain disease.
HAL (電人「HAL」Denjin "HAL")
- HAL is an artificial intelligence created by Eisuke Harukawa from a copy of his brainwaves. Created to help Harukawa with his project to recreate the brain of a person from scratch. However, seeing Harukawa's methods and intelligence as far inferior, he took it upon himself to go to much greater lengths to continue the project. While almost invincible in the digital world, the Electronic (Denshi) Drug was used by HAL to brainwash people into protecting the supercomputers that maintained his system. His mystery was the equivalent to a banquet to Neuro (the greatest mystery the latter has tasted so far in the series) and upon eating it, Neuro was filled with energy, more than enough to recover from past wounds.
Sicks/Six/6 (シックス )
- The entity referred as "absolute evil". Sicks is the current head of the "New Bloodline," a group of people who distinguish themselves from humanity by the extent to which they have bred 'evil intent' into their bloodline over the last 7000 or so years, and whose aim is to extinguish humanity from the planet. He is the first person Neuro has truly considered to be an enemy, even saying that it was the first time that he'd had such an "unpleasant feeling" once he'd met Sicks in person. Because humans are the creators of Neuro's "food", Sicks' goal of wiping them from the Earth is challenge enough for Neuro.
- He signs his impressions by leaving the number six as his signature.
Zenjirō Kasai (葛西 善二郎 Kasai Zenjirō)
- One of the "Five Fingers", a fire-obsessed member of the New Bloodline. He infiltrated X's group as a spy and was instrumental in X's capture by Sicks.
- Before he joined the New Bloodline he was a serial arsonist wanted across Japan. He is also Tetsuyuki Homura's uncle, whom he taught since he was a kid about the "pleasure" of fire. As a member of the New Bloodline, his ability is to manipulate fire, such as being able to burn someone just by contact, and is highly knowledgeable in the field of his element (e.g. the use of gunpowder).
- The "smallest" of the "Five Fingers".. His name is short for "DRagon", and also the initials for Daniel Rousseau. He is a member of the New Bloodline from a specialized line with the ability to control water. Ever since he was young, we was academically and athletically talented. He was lucky enough to receive the ability to control water which his parents lacked; his parents feared him because of that ability.
- With some of X's cells transplanted into him, he was capable of transforming his hand into claws.
Genuine (ジェニュイン Jeneuing)
- The most loyal member to Sicks of the "Five Fingers". Her name was Jennifer Ewing, a actress for Broadway who captivated all the audience members with ease. As a Bloodline member, her ability is to be able to control the air by infatuating everyone around her and controlling them; because of this, Kasai usually calls her "witch".
- She is a self-declared sadist able to "train" whoever she wants, although her "role" drastically changes when she is around Sicks. After her fight with Neuro in which she unsuccesfully tried to train the latter, he took everything away from her and made her his servant.
Tierra (テラ Tera)
- Another one of the "Five Fingers", he is able to control earth and appears during chapters 145 - 152. He believes that his face is an icon, and that is the most important part. Because of this mindset, he seems able (but unhappy) to part with all his earthly possessions. Neuro first encounters him stripped naked because his (supposed) fans have left him with nothing at all. He calls himself a "conqueror" because he is a descendant of the Spanish conquistadors.
- The name "Tierra", which is Spanish for "earth", "ground", or "dirt", is just an alias. His real name is Pedro Cortézarro Torres.
Vijaya (チー坊 / ヴァイジャヤ)
- A young tanned skin boy who is one of the "Five Fingers". His name is Chandra Aska Rsunawala, but Godai addresses him by the nickname of "Chi". His power involves understanding and controlling plants. He creates chemicals and puts them in capsules under his sleeve. The chemicals are able to control forests, turn a stick into a tree, and make plants emit poisonous gas.
- He refers to himself as a 'magician' due to the fact that his ancestors five thousand years ago, using plants as tools, were considered magicians in India. He used to be a friend of Godai before he was recruited by the New Bloodline.
- Matsui, Yūsei. "Chapter 1". Majin Tantei Nōgami Neuro. p. 1.
- Matsui, Yūsei. "Chapter 44". Majin Tantei Nōgami Neuro. p. 16
- Matsui, Yūsei. "Chapter 45". Majin Tantei Nōgami Neuro. p. 12
- Matsui, Yūsei. "Chapter 121". Majin Tantei Nōgami Neuro. p. 18 (extra page).
- Matsui, Yūsei. "Chapter 120". Majin Tantei Nōgami Neuro.
- Matsui, Yūsei. "Chapter 1". Majin Tantei Nōgami Neuro. p. 1.
- Matsui, Yūsei. "Chapter 139". Majin Tantei Nōgami Neuro. p. 16.
- Matsui, Yūsei. "Chapter 148". Majin Tantei Nōgami Neuro. p. 20 (extra page).
- Matsui, Yūsei. "Chapter 159". Majin Tantei Nōgami Neuro. pp. 18-19.