Manasa joined his uncle, Seta Tamanivalu, in debuting for the BNZ Crusaders in 2017.
Both boys grew up in Fiji and excelled at rugby there, with Manasa playing for the Fiji Under 18 team. He was also successful in athletics, winning medals in long jump and the 100 metre relay at the Fiji Secondary Schools Athletics Championships.
He followed his uncle to New Zealand at the age of 18 to take up a place at the Taranaki Rugby Academy. He played in Taranaki's sevens and Under-19 teams before being selected for the provincial team in 2016. He made an immediate impact, scoring a 50 metre try in his debut game against Hawkes Bay.