Sen'i coming directly from the Japanese for Fibre. In both Viz Manga, and the FUNimation dub, it is called the Fibre-Fibre Fruit. The fruit originated on a small island in North Blue, where it was found as treasure by some pirates who later lost it in a local town. Where it was discovered by a young boy who proceeded to eat it. The boy being the future captain of the Blue Haired Pirates, Johnathan Avery.