From MangaHelpers:
The weapons of the future, Metal Vessels, are being developed by different companies. One company, Sigma, has created a vessel that is controlled by two people-- a telepath and an anti-telepath. These two people are the teenage girl telepath, Yuiri, and her friend Io, an anti-telepath. They use their vessel mostly in demonstrations, such as competitive exhibitions with rival company Ciel's newest model.
While these vessels may seem to be the way of the future, the technology can also be very dangerous. A serial murderer is on the loose, who chooses targets through a website, and the police are beginning to suspect that the killer is actually using a Metal Vessel.