Japan had the game sewn up by half-time as goals from Yui Narumiya (pictured), Mizuki Nakamura and Rika Masuya put them in total control.
The victory maintained Japan’s 100% record in the six-team round-robin tournament, lifting them on to 12 points, three clear of DPR Korea.
And they have a better head-to-head record than their nearest challengers thanks to a 1-0 win over them on the opening day, meaning the championship is already in the bag with a game to spare.
The success continues a fantastic year for women’s football in Japan, whose teams have also won the FIFA Women’s World Cup and the AFC U-19 Women’s Championship.
Korea Republic now have a match against China on Sunday to decide who takes the third and final qualification spot for the FIFA U-17 Women’s World Cup next year.
Japan did not have to wait long for the opening goal as captain Narumiya gave them a fourth-minute lead, shooting inside the far post from the left of the area.
Masuya had a header tipped round the post by keeper Min Yu-kyeong before Japan doubled their lead in the 15th minute.
Japan were bossing the game and Masuya almost made it three only to stab a right-wing cross just the wrong side of the post.
She was on target in the 30th minute, though, running on to Ayaka Inoue’s through-ball and clipping her left-foot finish beyond Min.
Korea Republic already looked a beaten side and Masuya crashed an effort against the bar from outside the area.
Japan were cutting their opponents open almost at will and Ruka Norimatsu surged forward before chipping a pass in to Masuya.
The striker stretched to stab the ball past Min as the keeper came off her line, but her shot trickled just past the post.
Japan threatened to go further ahead at the start of the second half, but Masuya had a shot from point-blank range charged down.
The lively Masuya almost turned provider when she got to the byline but her cutback was hacked clear.
As Korea Republic waited to be put out of their misery, Japan were content to keep passing the ball around before the final whistle meant the celebrations could begin.