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.
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.