After a breakout first season in the Top League for NTT Communications Shining Arcs, Mafi was named in both the Tonga and Japan squad for the 2014 November tests.
[2] Mafi was then sidelined for eight months with a career-threatening dislocated hip injury but recovered just in time to make it back into the 2015 Rugby World Cup squad, where he again impressed.
Following the 2015–16 Top League season, he moved to England to join for Bath on a short-term loan deal where he was described as a 'sensation',[3] However his stay was ended early in controversial circumstances following an altercation with the club's medical officer.
Before Mafi's 2014 call up for the Brave Blossoms for his senior international debut against Romania he played in Japan's Kansai Collegiate Rugby Championships.
[5] On November 19, 2016, Mafi won the Man of the Match award in Japan's 33–30 loss to Wales at the Principality Stadium in the Under Armour Autumn Series.