The mysterious world of the Angels, their Angeloid servants, and the sinister Man of Synapse. It currently orbits over the Earth inside a sphere of disturbance high in the atmosphere. It comes to a stop over the town of Sorami after Ikaros falls to Earth and into Tomoki's life.
Located high int the upper reaches of the Earth's atmosphere, the mysterious and largely unknown world of Synapse orbits within a giant orb of disturbance over humanity. It is the vast home of the Angels, their loyal Angeloid servants, Angeloid creator Daedalus, and the powerful, sinister Man of Synapse; who appears to be one of the leaders of this mysterious realm. It's existence is largely unknown outside the scientific community (who feverishly study the orb of disturbance that it occupies as it orbits around various locations on Earth), but it is shrouded in mystery as to what takes place within. It is the world that the Angeloids Ikaros, Nymph, Astraea, Hiyori, Chaos, and the Harpies were created in, and where they obediently serve their masters under strict guidelines.
The realm of Synapse was created by Suu Minazuki for use in the Sora no Otoshimono manga. It is not fully known as to what inspired it's creation outside of the fact that it is where the Angeloids come from. Synapse first appears in Heaven's Lost Property #3 and Sora no Otoshimono: Volume Two.
Much is unknown about this mysterious world or it's angelic inhabitants, but the somber and shocking truth behind what really happens there under the rule of the oppressive Man of Synapse and his supporters is revealed by Eishiro Sugata's explorations and the revelations of Ikaros, Nymph, and Astraea. It consists of several massive floating islands that are inhabited by the angels and the Angeloids who tend to the gardens, chores, and other daily tasks. Up on the highest island in Synapse is the grand palace, where the Man of Synapse currently lives and where his followers go to attend meetings with their leader. His collection of Angeloid servants, the twin Harpies along with Nymph and the several nameless Pet-Class Angeloids who tend to his every need, is one of the largest in all of Synapse.
On one of the lower islands towards the far side of Synapse, Eishiro discovers a massive domed complex surrounded by a small forest in which the hundreds of Angeloid servants head into whenever their daily tasks ended with the ringing of a bell. Curious as to what is inside the building, Eishiro ventures within and to his shock and amazement, he discovers a massive room filled with thousands of metal and glass pods, each containing the slumbering forms of angels within. The Angeloid servants make their rounds of the circular room, tending to the rows of pods and to the sleeping angels inside. Eishiro, stunned by the discovery he has made and what this means, happens to come across a pod that contains a familiar figure within, the dozing angel of classmate Hiyori Kazane.