The metreon cascade was a weapon developed by the Haakonian scientist Ma'Bor Jetrel and used to devastate the Talaxian moon Rinax.
During the war between the Haakonian Order and the Talaxians, the Haakonians ended the conflict with a single weapon. The metreon cascade killed more than three hundred thousand people on Rinax, and many survivors later developed a lethal illness called metremia.
Years later its inventor, Ma'Bor Jetrel, contacted Voyager claiming to want to screen Neelix, who had been among those who saw the aftermath. His true aim was to test a method of reconstructing the victims using a modified transporter, an attempt to atone that failed.