Pini will race at 2:16pm Rio time (3:16am PNG time, Friday) and will swim in heat 2 of 6 of the butterfly event.
The world record for the 100 metres butterfly is held by Michael Phelps from the United States who set a time of 49.82 seconds back in 2009 in Rome, Italy.
Pini will be the fourth athlete from Team PNG to compete at Rio after Raymond Ovinou, Thadius Katua and Morea Baru.