[1] He was a part of the New Zealand Under 20s winning team over England Under 20s 64–17 in the 2017 World Rugby Under 20 Championship.
He made his Super Rugby debut for the Crusaders in their 34–20 win over the Chiefs in Round 16, 2018.
[2][3] Tima was named in the Highlanders 2020 squad after Connor Garden-Bachop had to withdraw because of injury.
In June 2021, it was announced that Fainga'anuku would be switching his international eligibility to Tonga using the Olympic loophole, representing Tonga Sevens at the 2020 Men's Rugby Sevens Final Olympic Qualification Tournament, however due to quarantining issues relating to the COVID-19 pandemic he was unable to play.
Fainga'anuku was re-called into the 'Ikale Tahi side for the 2024 end-of-year rugby union internationals, after leaving Manawatu to join North Harbour.