Secon Island is an island connected to Dock Island thanks to some Sea Train rails. Its main location is Kazanonsen, a large volcano that also appears to be a tourist attraction. There is a huge town beneath the mountain, dedicated to various hot springs.
As one of the three Endpoints, Secon Island acts as a seal to the vast quantities of subterranean magma underneath the New World. Should sufficient damage be inflicted onto this Endpoint, it will cause the volcano to erupt in a very devastating burst.
One Piece Film: ZEdit
Some time after the Straw Hat Pirates' first fight against Z, they learned that the Neo Marines were on Secon Island, and decided to go there via Sea Train (except for Franky, who stayed behind to guard and repair the Thousand Sunny) to get Ain to return Nami, Robin, Chopper and Brook to their normal ages. However, they failed to defeat him, and the island was eventually destroyed after the Dyna Stones Z planted near the island's volcano exploded.
- The island's name is a pun: When read with the Japanese suffix "-to" (島 island?), it can be read as the Japanese pronunciation of the English word "second" (セカンド sekando?), as the Japanese suffix "-to" can be read as "-do" due to rendaku. This refers to it being the second Endpoint shown.