Hollowire

The magictech that allows Wires to connect to the Hollow is typically known as a Hollowire, though it is also sometimes described as simply one's "connection" or "access" (not to be confused with access points within the Hollow).
A Hollowire consists of a cap that covers a user's skull and directly interfaces with their brain. No surgical or otherwise invasive procedures are required to use a Hollowire; the cap's magic allows it to send and receive signals to the brain without physical contact. These caps may be produced in a variety of different forms and designs to accommodate the many shapes of individuals Outside.
While using a Hollowire, an individual is completely oblivious to the Outside world and appears unconscious. Their sensory input has been replaced with input from the Hollow, and their motor output goes into the cap, to move their Hollow avatar, rather than moving their physical body.
While acquiring a Hollowire -- and therefore entering the Hollow -- is not free, it is widely available in many areas, some more than others. For a reasonable price, one can acquire a "Hollow starter kit" consisting of a Hollowire and Skincrafters' Guild services to set up one's starter avatar.
Many individuals hesitate to take advantage of this widely-available opportunity, however, due to the knowledge that entering the Hollow even once will land them there forever when they die and become an Echo.

Inventor(s)

Nesita & Delemont