Joji Obara was born as Kim Sung-jong on August 10, 1952, in Osaka, Japan, to Zainichi Korean parents. His father amassed considerable wealth through various businesses, including pachinko parlors and real estate, providing Obara with a privileged upbringing. He attended prestigious private schools and later graduated from Keio University with degrees in politics and law. After his father's death, Obara inherited significant assets and became a successful real estate investor, with his fortune estimated at around $38 million. However, during the 1990s economic downturn, he lost much of his wealth and was reportedly involved in money laundering activities for the yakuza syndicate Sumiyoshi-kai.

Between 1992 and 2000, Obara engaged in a series of heinous crimes, targeting women—particularly Western hostesses working in Tokyo's nightlife districts. He developed a pattern of drugging his victims with chloroform, rendering them unconscious, and then raping them. Obara meticulously documented his assaults, with police later discovering approximately 400 videotapes of his crimes, suggesting he may have raped between 150 and 400 women.

One of his earliest known victims was Carita Ridgway, a 21-year-old Australian model and bar hostess. In February 1992, Obara offered her a ride, during which he drugged her with chloroform. She was later taken to a hospital, where she died from liver failure and brain death. Initially, her death was misattributed to hepatitis E, and no investigation was conducted until years later when evidence linking Obara to her death surfaced.

In July 2000, Lucie Blackman, a 21-year-old British woman working as a hostess in Tokyo, disappeared after going on a paid date with a customer. Her dismembered body was found in February 2001 in a seaside cave near one of Obara's properties. Despite the gruesome discovery, the initial trial acquitted Obara of her rape and murder due to insufficient forensic evidence. However, in a 2008 appeal, he was found guilty of abduction, dismemberment, and disposal of her body.

Obara's trial began in July 2001 and concluded in April 2007, resulting in a life sentence for multiple rapes and the manslaughter of Carita Ridgway. The case garnered international attention, highlighting issues within the Japanese legal system, particularly concerning the handling of sexual assault cases and the treatment of foreign victims.