Saitama Wild Knights back Marika Koroibete scored three tries as the Japan Rugby League One champions rallied for a 51-20 victory over Yokohama Eagles on Saturday to set up a championship final next week against Kubota Spears.
The Australia winger's hat-trick and 24 points from the boot of Japan flyhalf Rikiya Matsuda helped the champions come back from a 17-5 deficit at the break, with Yokohama hampered by the red card shown to World Cup winning centre Jesse Kriel.
A red card was even more influential in Sunday's second semi-final at the same Prince Chichibu Memorial stadium in Tokyo, where Kubota Spears beat Tokyo Sungoliath 24-18.
Japan lock Hendrik Tui's early dismissal for a high hit on Kubota prop Kota Kaishi left his Sungoliath team mates with 14 men for the remaining 75 minutes of the contest.
Springboks hooker Malcolm Marx crossed to put Kubota ahead for good before the hour mark and Australia flyhalf Bernard Foley was named Man of the Match for his late try and three conversions.