"By the power of Nethys, my sister and I cannot meet... for as soon as one of us appears in the Material Plane

"By the power of Nethys, my sister and I cannot meet... for as soon as one of us appears in the Material Plane, the other one is immediately spirited away to our demiplane. There we sleep until it's time to switch back. The demiplane, by the way, is full of elemental energy, which is wonderful for restoring our strength."