Implanted against their will in Shadowspar Keep, each of the party members awoke at the beginning of the adventure with one of these in their brain. According to the party's current understanding, the purpose behind the devices is two-fold: it turns creatures who die with one still implanted into a zombie hulk, but also can explode inside the creature's brain, killing them instantly and destroying the device in the process. The explosion can happen at any time.
So far, the party's quest has revolved around finding a way to get these devices removed. Junpei Iori is the only one to succeed, albeit the hard way. Lord Milnor, while performing surgery on Junpei, deliberately triggered the device's defense mechanism, temporarily killing Junpei. Junpei's familiar then surfaced and brought Junpei back to life for a fee of 10,000 gold. Aludra, Thom, and Tum still have devices implanted.