For the in-game Note called "The Breach", see The Breach (Note).
The Breach refers to a vast, nebulous storm that exists between and links universes together. Though not fully understood, the Breach has proven to be passable, and many individuals have successfully navigated it to enter another universe. However, traveling through the Breach is highly dangerous and, without some form of protection or means of conveyance, such as a Breach Elevator, can be fatal. Though travelers have claimed to be able to see the Breach with the naked eye, the Breach itself may be invisible, and the effect seen in the sky is a jumbled molecular layer — a collection of random, glitch-like particles that fill the gaps where the Breach ends and another universe begins. 
Long ago, the people of planet Sudra were amenable to aiding travelers in their passage through the Breach using their advanced technology and by manipulating a device called the Breach Attractor. They built an elevator that would allow passage through the breach. However, the Sudrans' descendants over time became more and more religious, less knowledgeable of their own technology, more superstitious, and less amicable towards worlds and sentient species outside their own. As a result, the Sudrans became isolationist, using the Breach Attractor as a barrier to keep outsiders and intruders away and leaving the inhabitants trapped on Sudra. Rusalki cannot approach it, and with the Breach Attractor active can not pass the upper atmosphere. Elsenova mentons during the Power Filter cutscene that "There are two sides to universe - Worldstream and Breach. Breach is like storm - deadly, cannot be pass.". Eventually, the Sudrans lost almost any understanding of what the Breach is, instead perceiving it as a meteorological phenomenon.
Scientific Theories Edit
Athetos theorized that the Breach is a mesh that links adjacent universes, and through his revolutionary development in a new branch of physics, he is able to traverse the Breach, leaving Earth and reaching Sudra on the other side. Athetos Variant 7 further hypothesized that the visual effect of the Breach which can be seen in the upper areas of Kur and Edin is actually invisible and that "a protective field of microscopic elements covering the frayed ends" is being seen.