Niiyama was born in
Aomori. She was previously married to baseball player
Satoshi Kuroda in 2004. Together, they have a daughter named Koharu Niiyama, born on July 12, 2006. They divorced on December 29, 2014. On November 7, 2023, Niiyama announced her second marriage to a non-celebrity man, who is thirteen years her junior. They have reportedly been in a relationship for five years. ==Filmography==