The American, who entered the competition as a qualifier, becomes the youngest player to reach a WTA final since 2013. She will face Su-Wei Hsieh on Sunday after the No. 2 seed beat Qiang Wang in an all-Chinese semifinal.
With a world ranking of 41, Shuai was the favourite to win the title in Hiroshima but Anisimova, who turned 17 just two weeks ago, was the surprise winner.
“She’s definitely a tough player, one of the toughest I’ve played,” Anisimova told the WTA website. “Overall, the match was really good — it was super-close and I was fighting for every point.
“I was just focusing on myself, that’s what I always do. As the match goes, then I just see where her weaknesses are and how to play against her.”