Ylapu is a strange, floating island suspended 2500 meters over Leazas. The records of its creation have long since been lost, so for years it was shrouded in mystery. In reality, it is a floating battle fortress known as a "Toushin Toushi", created by the Holy Magic Sect to fight Demon King Gi. Its codename is "Toushin Toshi Upsilon" (or just Toushin Toushi Y).
In the events of Rance IV, the island crashed in the southern part of the Free Cities zone, and a city was founded from its ruins. In the future, this city is known simply as Toushin City, and is the main setting of the Alicesoft's series simply called Toushin Toshi.