As news of her death reached Italy, her Instagram account was flooded with tributes.
“The sea, that gave you so much, has taken your life. Rest in peace,” one Italian wrote.
Another wrote: “I just heard the dreadful news. RIP.”
Manfrini was from the town of Venaria Reale, where her father was a lawyer and her mother a doctor.
Fabio Giulivi, the Mayor, said: “The whole community offers its condolences to her family”.
“The news of her death has shocked us all, we feel helpless in the face of a tragedy that cut short her life so prematurely.”
Manfrini graduated in law but forged a career initially as a snowboarding coach. She then developed an interest in surfing and moved to Bali, where she worked as a surfing instructor.
Officials planned to transport her body by boat to the port of Padang on the west coast of Sumatra, from where it would be repatriated to Italy.
The Mentawai islands are one of the most renowned surfing destinations in Southeast Asia.
In an interview with a website called the Salt Sirens in 2019, Manfrini said: “Surfing wise, I love the wilderness of North Sumatra – the rainforest there is so primordial and gorgeous. I love sitting in the line-up with few friends, listening only to the sounds of the jungle, and waiting for a set which I already know will be perfect and will deliver some barrels.”
Human fatalities from swordfish are highly unusual and extremely rare. Swordfish are found in temperate and tropical waters around the world, and an adult swordfish can grow up to 4.5m-long and weigh about 450kg.
In 2015, a fishboat captain in Hawaii died after being impaled by the bill of a swordfish.
Randy Llanes, 47, jumped into the water to spear the fish but it then struck him in the chest.
By the time he was taken to hospital, he was dead. The swordfish was about 1m-long with a bill that was about the same length, Hawaiian officials said.
“Swordfish attacks on humans are extremely rare, but they can kill if vital organs are involved,” scientists said in a report published by Science Direct in 2007.