Japan made sure of its sixth straight HSBC Asian 5 Nations title when it trounced South Korea 64-5 at the Prince Chichibu Memorial Rugby Ground on Saturday.
Takashi Kikutani's try in the 23rd minute — Japan's fourth — brought up the bonus point Japan needed to ensure it cannot be overtaken in the standings even though it still has a game to play.
"We've got one game left but we are the champs so we have completed the first challenge of the season," said Japan coach Eddie Jones.
"I am very pleased with today's performance. It was a good first 40 minutes and although we got a little bit tired in the second half and were a bit flat, we finished well."
Kikutani added a second try to take him to 28, the most by a forward in test-match rugby, but it was Japan's young backs that dominated the rest of the scoring.
Kenki Fukuoka grabbed a brace and there were five-pointers for Yoshikazu Fujita, Kosei Ono, Male Sa'u and Ayumu Goromaru with Hendrik Tui and a penalty try ensuring the forwards' hard work was rewarded.
"The Japan players were quicker than we expected and we just couldn't cope early on," said Korean captain Park Soon Chai.
On a glorious spring day in the nation's capital, flyhalf Ono gave Japan the ideal start going over with just 90 seconds on the clock.
Fukuoka showed great speed off the mark to score five minutes later when he was put away in the narrowest of gaps by Fujita, before the 20-year-old added a second three minutes later.
A great steal by the Japan pack close to its own line allowed Atsushi Hiwasa to launch a counter-attack and Fukuoka's speed did the rest. Goromaru added the extras as Japan led 21-0.