Prior to December 2017, Ainuu played rugby for Seattle Saracens in the CDI Premier League. In December 2017, Ainuu signed a six-month academy contract with Toulouse in France's Top14. (Ainuu had previously agreed to join the Seattle Seawolves for Major League Rugby's inaugural 2018 season, but ended that agreement before the season began in order to play at the higher-level of competition.) In September 2018, Ainuu re-signed with Toulouse, committing to the club through the 2020–21 season. Ainuu made his Top 14 debut for Toulouse on 23 September 2018, appearing as a halftime-substitute in a 66–15 defeat to Montpellier.