Sharaku Homonji (Yuji Oda) is the eldest son of a distinguished family who has studied crime for generations. The eldest son from the Homonji family has tested for an IQ of 246 for generations and Sharaku Homonji possess an IQ of 246.
Soko Wato (Tao Tsuchiya) is a detective. One day, she is assigned to the investigation section #1. Her job there is not to investigate crimes, but to escort Sharaku.
Detective Keita Kurokouchi (Tomoya Nagase) continues to extort money from politicians whom Keita Kurokouchi has information on. By using his information he is able to crack unsolved cases. Rookie Detective Mayo Seike (Ayame Gouriki) is excellent with her job and also a bit naive. She conducts an internal investigation on Detective Keita Kurokouchi, but they become partners and work on cases together.
Kazuko Yamase (Aoi Morikawa) is a 23-year-old, broken-hearted freeter. One day, she sees a knitted teddy bear that really appeals to her. She decides to buy it. Later, the knitted teddy bear suddenly speaks! Within the teddy bear, Yasuo Amano's (Sho Aikawa) spirit lives. He is the person who knitted the teddy bear and he was also detective. Kazuko then becomes involved in a case with Yasuo and helps to solve the case.
Rena Sasaki (Keiko Kitagawa) is a beautiful woman with excellent memory and intelligence. She becomes a private detective and risks her life to chase down evil private detectives, because her younger sister was murdered by a stalker. The person that provided information to the stalker on her sister's location was a private detective.
Shinobu Satomi (Tori Matsuzaka) works in the Mobile Investigation Unit of The Tokyo Metropolitan Police Department. The Mobile Investigation Unit conducts the initial investigation at all crime scenes. He works with Yuki Inokuma (Fumino Kimura). They are a couple, but they keep their relationship a secret at work. They both hope to work at the #1 Investigation Station. One day, they meet beautiful Kara Tachibana at the site where a dead body was found. Kara Tachibana appears at the other crime scenes involving grotesque murders. She shows an interest in Yuki Inokuma. Shinobu Satomi thinks it's a bad sign for Yuki Inouma. To protect his girlfriend from danger, he struggles to find uncover the truth behind the serial murder cases and Kara Tachibana’s identity.
Haruya (Yuta Tamamori) is a university student. He is smart, brave and curious. Haruya then becomes involved in a case and investigates like a private detective. Since then, Haruya works like a private detective to solve cases.
Ikuo and Tatsuya are orphans. They live at Mahoroba’s house which is a child and family services home. At their elementary school, they see Teacher Yuko, who took good care of them like a real older sister, killed right in front of them. Ikuo and Tatsuya tell the police what they saw, but the case is covered by a police officer wearing a gold watch.
15 years later, Ikuo (Toma Ikuta) now works as a detective. He is a good person and his arrest rate is the highest at the police station. Meanwhile, using his handsome appearance and cleverness, Tatsuya (Shun Oguri) becomes a high ranking yakuza.
Detective Ikuo and Yakuza Tatsuya have a singular purpose, which is to find the man wearing the gold watch, dig out the truth and reveal the dark side of the police organization.
Nagisa Kinomiya (Maki Horikita) is a detective for the 7 Investigation Division. The team consists of female detectives and they seek out female criminals and to help female victims. Nagisa Kinomiya has a special ability to hear the mind's of others. To shutout other people's emotions, she wears a headset, but, when working on a case, she uses her special ability. At crime scenes, Nagisa Kinomiya can hear the left behind voices of criminals and victims.
Light Yagami (Masataka Kubota) is an ordinary university student. One day, he receives a death note which changes his life. The death note awakens his warped sense of justice and genius. He becomes murderer Kira and punishes criminals.
L (Kento Yamazaki) is a well known private detective. L appears in front of Light Yagami. L defines Kira as evil and decides to catch Kira. Then N (Mio Yuki), who has a beautiful appearance but dangerous existence, appears.
Eisuke Tameyori (Hidetoshi Nishijima) is a middle-aged private practice physician. He has the ability to diagnose someone's condition just by looking at their appearance. He is also able to recognize people who will commit crimes in the future by certain symptoms and tries to prevent them from committing those acts. He meets Detective Junichiro Hayase (Atsushi Ito) and they soon work together to solve cases.