The former under-20 Australia player could also play trial games for the Wild Knights while based in Kumagaya until early November before returning to Queensland for off-season games against the League One team, the Reds said on Monday.
The deal is similar to an arrangement with Benetton Treviso which saw several Reds players seconded to the Italian club after the 2025 Super Rugby season.
"Locking in my future for 2027 is great and the Reds creating cool chances like this in Japan is definitely something you don't get at other clubs," said Rubens.
"I jumped at the chance in Japan.
"Rugby comes first with developing my skills but I also want to experience a different culture and view on rugby."
Rubens made his Super Rugby debut against the NSW Waratahs in the 2026 season opener and has had three appearances for the Reds as a winger.
He returned to his local side Souths and enjoyed a big season in the Hospital Cup, Queensland state's top club competition, finishing as the top try-scorer (15) as a line-breaking outside centre.
With Australia centre Hunter Paisami set to join Shizuoka in Japan, Rubens may have more opportunities in the Reds' midfield in 2027 under Vern Cotter, Les Kiss' replacement as head coach.
"I play outside centre at club but you keep all doors open so I work hard at wing as well ... Training all season at the Reds with Wallabies centres like Josh Flook and Isaac Henry has really helped show me the stamp I need to make on a position," Rubens said.
The Reds have been enthusiastic about giving developing players a taste of international experience during the off-season.
Scrumhalf Louis Werchon returned to the Reds after his Benetton secondment and played 13 games in the 2026 season, his best campaign for the Queenslanders.
With two Wallabies halfbacks in Tate McDermott and Kalani Thomas ahead of him at the Reds, Werchon has since signed full-time with the Italian club on a two-year deal, but the Reds are hopeful of luring the 23-year-old back to Queensland eventually.