Watanabe is a Japanese citizen who was visiting Hawaii in the spring of 2007. She was staying with a host family and volunteered at Sunset Beach Elementary School. She was last seen between 9:20 and at 10:00 a.m. on April 12, 2007, walking on Pupukea Road. Witnesses saw Watanabe get inside a Hauoli Termite and Pest Control truck at the Pupukea Foodland. The vehicle was being driven by a Caucasian man. Watanabe looked "confused" at the time and was not speaking to the driver, although he was speaking to her. She has never been heard from again.

Later that month, Kirk Matthew Lankford was charged with Watanabe's murder. Photographs of Lankford are posted below this case summary. At the time of her disappearance, he had worked as a technician for the pest control company, although he was later fired. He was working in the area on the day Watanabe disappeared. Authorities found Watanabe's blood and her eyeglasses in Lankford's company truck, and the windshield on the passenger side was cracked. Lankford claimed a bird had caused the damage. A witness reported seeing a man digging a hole near Kahana Bay at about midnight on April 12. The man claimed he was looking for a gold chain he had lost. The witness wrote down the man's vehicle's license plate number and it matched Lankford's personal truck, and the witness later identified Lankford in a police lineup. Lankford's wife stated he left the house that evening, saying he was going to work a side job, and when he returned his socks were muddy. She later recanted her statement.

Lankford has no criminal history and is described as deeply religious and a devoted father and husband. The indictment charges him with second-degree murder and accuses him of either knowingly killing her, or knowingly harming her and allowing her to die without rendering aid. If convicted, he could face life in prison.

Watanabe is described as a shy, artistic young woman who loves drawing, especially dogs and other animals. She normally lived with her family on rural Sado Island in Japan. Her body has not been recovered, but foul play is suspected in her disappearance due to the circumstances involved.