Rokkenjima

Rokkenjima (六軒島?, lit. "Six House Island") is a small island located off the coast of Tokyo in the Izu archipelago. It measures about 10km around. The majority of the island is covered with a dense forest, with the exception of areas of land developed by Kinzo for the mansion.

History
The island was used in World War II as a military base for the Japanese army. It was meant to serve as a launching point for the navy's Kaiten torpedoes, but was never supplied with them due to the nation's poor financial state, and eventually forgotten by the military command. In 1944, Kinzo was stationed on the island as a soldier when the island came into contact with a submarine containing soldiers from the Italian Social Republic. It is during this incident where he met Beatrice Castiglioni and acquired the legendary ten tons of gold. A gunfight eventually broke out between the Japanese and Italians over the possession of the gold, leaving Kinzo and Beatrice as the only survivors.

The island was then purchased by Kinzo from the Tokyo metropolis utilizing his connections with the GHQ. It was acquired under the pretext of establishing a military base, but then converted into Kinzo's own personal island. The island was then developed, with the mansion constructed in 1952. Kinzo's wife and children moved onto the island with him, and the residence of the island eventually shifted to Krauss's family.

After the events on October 5, 1986, the island was repossessed by the Tokyo Metropolis and sealed off from the public.

Rokkenjima Incident
The Rokkenjima Mass Murder Incident (六軒島大量殺人事件 Rokkenjima Tairyō Satsujin Jiken?), also known as The Rokkenjima Eighteen Murders and The Witch's Legend Serial Murders Incident, refers to events as the name suggests the massacre of the Ushiromiya family and the people in Rokkenjima during October 4 and 5 of 1986.

Official Story
During the Ushiromiya family conference, it is believed that a massacre took place. This was supported by the fact that everyone did not return and there is evidence that there was a huge explosion that took place. It is believed that the motive behind the murders was the fight over the gold that Kinzo Ushiromiya possessed. The case was not solved and several years later two message bottles were found that details the events that transpired. However, the problem was that the order of murders that took place were different, adding more to the mystery of the incident as well as adding interest to the public. The only thing that was certain was that both messages were signed with Maria Ushiromiya 's name and both had the same handwriting, meaning that both were written by the same person. Later on a piece of Maria Ushiromiya's jaw was found as a result of the police investigation. Other parts of her body weren't found and neither of the relatives as well and it was hopeless to think that anybody that attended the family conference was still alive. Despite the contradictions, interviews with servants from Rokkenjima confirm that the author knew the mansion and its inhabitants in considerable detail. The only known survivor was Eva Ushiromiya believed to have been the culprit.

Season 3
Small portions of Rokkenjima Mansion are shown in lore, but this is just the Meta-World fabrication of Rokkenjima. The final fight between Ushiromiya Battler and Agent 47 takes place in the Secret ring of Rokkenjima in the Meta-World.