Ryouka's real name is Aveline Narusawa Tesla. She is the daughter of Nikola Tesla. Aveline's real body died a long time ago, but lives on as an astral body, in other terms, as a ghost. She is the person who was giving orders to Yuuta Gamon the entire time. She is very knowledgeable about what a ghost truly is:
"The soul, in other words, electromagnetism with memories and personalities, is the astral body."
She explains to Yuuta about how Yuuta was able to do everything that he was able to do, like why he was able to send text messages and still communicate with the outside world. What he was doing was all through radio waves.
Ryouka eventually became Yuuta Gamon's "minion" because she saw that Yuuta actually has special powers involving the "astral world."
The gun that Ryouka owns is actually called the Wardenclyffe Gun. It was a machine created by Nikola Tesla, it is an important item that serves as the key to the New World System. It was a small prototype of the Wardenclyffe Tower that Nikola had erected on Long Island, New York. Tesla's World System is theoretically able to make the wireless global supply of energy possible. The Wardenclyffe gun is a machine that replenishes the electromagnetic force in the body forever, also known as eternal life.
