The Nexus is the central hub of the dream world.
The Nexus serves as the first room outside of her own room in Sometsuki's dream world. There are eight doors in this area which, starting from the top left and going clockwise, will take Sometsuki to Pastel World, Old Storehouse World, Cyber World, Macabre World, Seabed, Boreal Forest, Ancient Ruins, and Snow World.
Not much changes in this area, however, if the Distorted Cyber World event has been activated, the Cyber World door will change appearance to have square patterns on it instead of rectangles. This is easily reset by simply waking up.