All Black Richie Mo'unga picked up a winner's medal in his first season in Japan after leading Brave Lupus Tokyo past Saitama Wild Knights 24-20 in Sunday's championship final.
The New Zealand fly-half moved to Tokyo on a three-year deal after playing in his country's narrow Rugby World Cup final defeat to South Africa last year.
He won Super Rugby titles with Crusaders in each of the last seven years and he added to his collection in front of more than 55 000 fans at Tokyo's National Stadium.
Saitama were looking for their third title in four seasons but Tokyo pulled off an upset, with substitute Yuto Mori scoring a late try to settle a back-and-forth contest.
Saitama thought they had won it in the last minute but Tomoki Osada's try was scrubbed off after a video review found a forward pass in the build-up.
Tokyo's Jone Naikabula scored tries either side of halftime before Ben Gunter and Taiki Koyama both crossed the line for Saitama.
Saitama made their intentions clear straight from the kick-off, camping out on Tokyo's try line but just failing to apply the finishing touch.
Rikiya Matsuda got Saitama on the board with two penalties but Tokyo came roaring back when Japan international Naikabula bounced two defenders out of his way before touching down in the 27th minute.
Mo'unga converted the try to put Tokyo ahead, and the fly-half extended their lead with another penalty before halftime.
There was more bad news for Saitama when Australian international Marika Koroibete was sent to the sin bin for hauling Naikabula down by the collar as he charged for the line.
Tokyo took advantage early in the second half when Naikabula raced through for his second try and Mo'unga added the conversion from the touchline.
Mo'unga missed a penalty with 20 minutes remaining and Saitama punished his team when Gunter went over for a try in the corner.
Koyama then put Saitama in front with another try in the 68th minute, and Matsuda added the conversion.
But substitute Mori had the last word, touching down to reclaim the lead for Tokyo, who held on for the title despite Osada's late scare.