Ianthe is the main power source of the planet, Altair. Created by Oriza, the mother of Izumo Kamurogi, this device draws out the power from Altair itself. Due to having too much power being drawn out from planet, the planet itself takes away the ability to give life from the creatures on it to conserve energy, resulting in what is known as "The Curse of Eve." This curse either causes all female lifeforms to die or ultimately adapt to it by changing their minds and bodies into the body of a male in order to survive.
The only way to break the curse is to use a Rare Iguras (a female who can withstand inter-dimensional travel and is capable of maintaining her female form whilst in Altair).
However, the repeated trips to Vega ultimately caused Ianthe itself to start malfunctioning due to the heavy power drain that's required to power the Inter-Dimensional Transport Device.