Onozuka, who also won World Championships halfpipe bronze back in 2013, scored 89.80 to take gold, with Marie Martinod of France settling for silver and American Devin Logan taking third.
Logan was followed by team-mates Annalisa Drew and Maddie Bowman in fourth and fifth respectively, before British Rowan Cheshire finished sixth.
Fellow Brits Madison Rowlands and Molly Summerhayes were 11th and 15th respectively.
In the men's event, American Aaron Blunck followed up his X Games SuperPipe gold by taking the World title too.
Blunck scored 91.80 points to take the crown, with Canadian Mike Riddle and Kevin Rolland of France second and third respectively.
Murray Buchan was the highest-finishing Brit in 16th, with compatriot Peter Speight two places further back.
Read the original article on Eurosport: Onozuka and Blunck claim halfpipe world crowns