Tanegashima Island

Tanegashima, also known as Tanegashima Island, is believed to have been one of the few islands nestled within the Ōsumi Archipelago before it's mysterious disappearance.

History
Tanegashima was the easternmost and the second largest (after Yakushima) of the Ōsumi Islands. It was located approximately 43 kilometres (23 nmi) south of the southern tip of Ōsumi Peninsula in southern Kyushu, or 115 kilometres (62 nmi) south of Kagoshima.

Prior to the formation of the Union, the island had been used by the Japanese Space Agency (JAXA) for both launching ballistic rockets and space research; it was eventually seized by City 8 and declared off-limits, along with the rest of the Ōsumi archipelago. Due to the intense activity of nearby cessation zones, it was never touched by any of the various new nation-states after Liberation, and sat undisturbed for decades.

In 14 A.L, it is rumored that Rubin Locke set out to invade the island with the assistance of Jiroaki Kudo, a high-ranking Urban Defense Department official and backed up by an entire UDD division, including aerial gunships. The precise reason for why is unknown, but given that the island has since disappeared and none of the involved participants have ever publicly resurfaced in subsequent decades, it is whispered that the rogue group intended to seize the island to 'tunnel a pathway to Mars', Tangeshima having since been revealed as the site of early Unionized teleportation experiments. Some historians believe that Locke had access to the island during his Civil Board employment, but this is without historical evidence and based solely on his alleged familiarity with both the island and supposed technological infrastructure displayed during his final speech at an emergency session of the Lambda Seat.

Tanegeshima's existence is denied by both the Zaibol and East Lambda governments, but this is attributed to a mutual agreement withhold what information is known than genuine belief in it's non-existence. Free Russochina has declared their intention to investigate the disappearance in the future, but with the war between itself and the UTCE in a stalemate, this has not been initiated yet. Deceased Generation One transhumans have been found scattered around the archipelago since then, but their dramatically-aged state and questionable condition has made it impossible to verify much of the rumors, instead leaving yet more questions.

Much like the ancient site of Area 51, Tanegashima is often featured as a 'lost city' of mysterious, abandoned and potentially lucrative technology thought gone forever in various urban stories and rantings, and attributed as the linchpin for all sorts of conspiracies, most involving Locke and the fabled 'Mars Colony'.