It's October 4th,1986 and the wealthy Hiragi family is gathering for their annual reunion at Rokkenjima island, in order to discuss what will happen to Hiragi Tenri's inheritance, since it's rumored that he will die soon. Yuichiro, a 16 year old boy, has returned to the family after 6 years to meet again with his friends. While the arguments about the inheritance proceed, a typhoon traps 18 people on the island. The members then find a mysterious letter from a person claiming to be Tenri's alchemy councilor, the Golden Sorcerer. Unless someone in the family solves an epitaph that has been left for them, the Golden Sorcerer will claim everything that the family owns and also it will lead to a series of events that nobody expected. Or, the Umineko!AU that no one asked for.