Tupou back with Sunwolves
The centre previously played for the Western Force in Super Rugby before heading to Japan to play for the Coca-Cola Red Sparks and the Sunwolves.
Tupou was also a former Tongan Rugby League international before he made the switch to Rugby Union.
The other two additions to the Sunwolves squad for 2018 are Yutaka Nagare from Suntory Sungoliath and Hosea Saumaki from Canon Eagles.
The Sunwolves start their 2018 Super Rugby campaign against the Brumbies in Tokyo on February 24.