Born in 1972 in China, Zheng Yongshan moved to Japan in 1999 and married a Japanese man, adopting the name Mie Taniguchi. The couple had a daughter and settled in Nagahama, Shiga Prefecture. Despite efforts to assimilate, Zheng reportedly faced social isolation and difficulties integrating with other local mothers. ​

On February 17, 2006, Zheng was responsible for driving her daughter and two of her daughter's kindergarten classmates, Wakana Taketomo and Jin Sano, both aged five, to school as part of a carpool arrangement. During the drive, she used a 20-centimeter sashimi knife to stab the two children multiple times—Taketomo 19 times and Sano 13 times.

After the attack, Zheng disposed of the children's bodies in rural areas of Nagahama. Taketomo's body was found on a country road, while Sano's was discovered in an irrigation stream. Zheng was later found with her daughter in a parked car 56 kilometers away, still in possession of the bloodied knife. ​

Zheng was arrested the same day and charged with murder. During her trial, she claimed that her daughter had been bullied by the victims, a claim the court found unsubstantiated. The court acknowledged that Zheng was in a state of diminished responsibility due to a diagnosis of schizophrenia but determined she had a strong intent to kill. On October 16, 2007, she was sentenced to life imprisonment, a sentence upheld by the Osaka High Court in 2009.