The Harmsway is a device that is used to heal the Reckoners. It is shown to be very effective against everyone but Megan because Epic powers cannot be gifted to other epics, excluding Calamity's powers.
Cody refers to it as "the last of the three [pieces of Reckoner technology]", with the other two being the Tensors and Jackets. It is later revealed these devices do absolutely nothing and actually Prof gifts his healing powers to the Reckoners.
Later, Knighthawk uses Prof's cells to make a real harmsway, which is used to make a suit that mimics Prof's power portfolio.