Spring-Heeled Joplin (バネ足ジョップリン Bane ashi Joppurin) is the Artificial Island's very own living urban legend.
Originally implied to be just one person, it is revealed that Spring-Heeled Joplin is really a large loose network of various persons (all of whom refer to themselves as "Spring-Heeled Joplin" when talking to each other via text or audio).
The "brain and spinal cord" of Spring-Heeled Joplin is said to be back on Japan's mainland (in the Kanto region). It is unknown who exactly this person is, but it is possible that he is the Joplin who frequently irritates Yakumo Amagiri. This Joplin usually has a radio attached to something - a tin toy or a cat - and he sends the toy and/or animal Yakumo's way and proceeds to chat with him. He makes the tin toys himself. He uses cats as carriers because he knows Yakumo is so fond of them he will not harm them.
His room contains countless screens and radios, each "endlessly spewing information."
This Joplin - the brain and spinal cord - originally founded Spring-Heeled Joplin as part of a promise made with Yatsufusa, the first DJ of Sōsei Airwaves. Yatsufusa declared that he would go around the island and 'create a flow.' He claimed that the job of his friend (the Joplin) was to figure out the flow from an outside perspective and control its direction. The original Joplin proceeded to sever his ties with his family, his past, and society in general, and started to Observe the island.
He chose new Joplins himself. People who stood out even on the island, or those completely isolated from society (and thus unlikely to spill the secret). If someone revealed their identity, it was immediately reported to the rest of Spring-Heeled Joplin. After Yatsufusa's death, the original Joplin decided to make Spring-heeled Joplin grow as an urban legend "for the sole purpose of inheriting the will of Yatsufusa.
In the words of Yakumo himself: "He appears everywhere on the island to give advice to some and warnings to others. From the way he talks I think he might be a foreigner, but it also kind of feels like he's doing that on purpose. He is a fickle creature that points a starving runaway girl to a way out of the island's labyrinth, but at the same time leads curious reporters and their sort to the casino or The Pits to bring them to cruel ends."
The islanders have very little grasp on what Joplin actually is. They tend to blame mysterious or unexplainable incidents on him, saying "blame it on Joplin" as though referring to a fairy or imp.