
Detective Ukyo Sugishita confronts crime on the basis of his own convictions. He has a partner that works for him in the Special Task Unit. For the first 7 seasons, Ukyo’s first partner is Kaoru Kameyama. He is a good-natured, hot-tempered, straightforward and somewhat scattered detective. Beginning in Season 8, Takeru Kanbe replaces Kameyama. Contrary to his predecessor, Takeru is a lanky, cool, conceited and confident detective. From Season 11 to Season 13, Ukyo’s partner is a young detective Toru Kai. Toru is a son of Deputy Director-General of The National Police Agency. But he became a detective by his own effort. And starting with Season 14, Ukyo’s current partner is Wataru Kaburagi, an elite bureaucrat who came to the Metropolitan Police Department on temporary assignment. As the first partner without any career of a police officer, he will face challenging cases together with Ukyo.

Satoshi Itomura is an assistant police investigator who belongs to the Metropolitan Police Department’s Scientific Investigation Team. Reenactments, fingerprint and voice data collections, profiling... His team collects scientific evidence and pieces together fragments of information in order to help build evidences. However, Itomura often does not care about the scientific approach and instead pays a great deal of attention to the things that the victims always carried with them or treasured. And he focuses on these things because they usually carry the victim’s dying wishes, understanding that last message not only helps solve the cases but also brings closure to the depressed family of victims.

A Japanese girl from a poor family named Hanako went on an adventure to study in a girl's Christian school in Tokyo. She found her passion in English and step by step made her dream come true.

Yuri Ishikawa and her team try to crack unresolved cold cases in Kanagawa Prefecture, Japan.

Yukiko Makabe works at the #3 Special Investigation Team of the Metropolitan Police Department. She has excellent negotiation skills. Yukiko then attempts to negotiate with a hijacker on a bus, but something unexpected happens and her mission fails. Yukiko takes full responsibility and takes a transfer to a special interrogation team "Kintori". Her boss is Katsutoshi Kajiyama and Yukiko has had a difficult working relationship with him in the past. Her other coworkers include Susumu Hishimoto, Zenjiro Nakata and Haruo Koishikawa.

Shūichirō Kiriyama works at the Limitation Task Force, the place where the cases which have reached the statute of limitations are destroyed. Getting bored of his job, he decides to find a hobby, because it seems important to him to have a hobby. So he decides to puzzle out the unsolved cases on his free time, helped by his coworker Mikazuki, who seems to have a crush on him.

Narrates the events and cases encountered by Kaoru Utsumi, a rookie detective, and Manabu Yukawa, a university associate professor, while the two pair up to solve many mysterious cases.

University student Kuno Totono is the type who constantly questions what is taken for granted in society and develops his own theories based on his vast knowledge and unique set of values. One day in autumn, the police come to see him. His university schoolmate has been murdered at a park nearby and the police apparently regard Totono with suspicion. He is asked to come with them for questioning. In the interrogation room, the police are manipulated by Totono who tends to digress from the topic and poke at their contradictions. He even correctly guesses that one of them is troubled about not getting along with the wife and ends up giving advice. However, Totono’s fingerprints are eventually discovered on the murder weapon.

Hanasaki Mai is but an ordinary employee of a bank, with zero diplomacy. She doesn't think twice about pointing out her boss' mistakes. Her job is to investigate any wrongdoings in the bank branches. She is the voice of the suppressed staff who are unable to go against their bosses. Her partner is the veteran staff, Soma Ken, whose career with the bank had reached a dead end, no promotions in sight. Together, they resolve all the non-compliance issues at the bank.

A random mass stabbing, major food company Titus Foods, and a mysterious infant disease. These three things have as much in common as Detective Soma, hack writer Yarimizu, and the stabbing's lone survivor, Shuji. Yet, these men are now embroiled in a risky quest for the truth. What they find, though, is more heinous than they imagined, making them question just who is the real criminal?

Mike Hama, Private Detective, is a chain-smoking, wisecracking tough guy with a weakness for the ladies and a soft spot in his heart, especially for his kid sister Akane. Mike's so down on his luck he'll take any case, from finding a lost pet to spying on cheating spouses. But every now and then, along comes a client with dubious and dangerous case… and that's when Mike shows his stuff.

Inami and Tamaru work at the Public Security Mobile Investigation Unit Special Investigation Team, a team made up of specialists with different expertise. Inami tackles criminals with showy maneuvers, while Tamaru corners criminals with cool calculation. Together, the team tackles terrorists, new religious cults, military spies, secret narcotics organisations and complicit politicians.

Hitsujitani Chiharu joined a big advertising agency after she graduated from a university. She experienced a hard time at her job due to harassment. After 3 years, Hitsujitani Chiharu decided to quit working at the advertising agency. She begins to work for a temp agency that is run by her aunt. There, she meets Kurusu Arashi, who works as a career adviser at the temp agency. He walks with a cane due to discomfort from his left foot, but he has a great reputation as a career adviser and his nickname is The Devil of Changing Jobs. He often makes biting remarks to people worried about changing jobs. Working with Kurusu Arashi and dealing with people who are looking to change jobs, Hitsujitani Chiharu also grows as a person.

"Ouroboros" is an ancient symbol that depicts a snake eating its own tail - meaning infinity. Based on a popular comic, a clumsy detective and a cool gang stand up to true evil. Ikuo and Tatsuya grew up in a children's orphanage together. When their favorite teacher, Yuiko, is murdered, a policeman wearing a gold watch covers up the incident. Ikuo and Tatsuya promise each other to avenge their teacher someday. Twenty years later, Ikuo is a detective in Shinjuku second police station investigating various cases with elite detective - Mizuki, while smart and handsome Tatsuya has become one of the top members of a gang group.

Saburo is a high school student good in sports, but not very good with his studies. One day, Saburo travels back in time and arrives in the Sengoku period of 1549. There, Saburo meets Nobunaga Oda who looks and sounds just like Saburo. Nobunaga Oda is the son of a warlord and magistrate of the lower Owari Province. Nobunaga Oda though is physically weak and he asks Saburo to take his place. Then, Saburo as Nobunaga Oda attempts to unify the country of Japan.