Vessel (state)

A Vessel is a human spirit that is so corrupted by "evil" (or perhaps sin) that they are capable of being remotely controlled by a demon, and forced to act in their stead, with varying degrees of awareness. It is implied that an abundance of evil carried in the soul interferes with the human right of free will, making them easier to compromise. [Source: Frederike (1/30/18)]

Being a Vessel is similar to being a human susceptible to involuntary possession or channeling; the target has no choice in the matter, and sometimes, retains no memory of what happens. Others remain completely aware, but unable to prevent their actions.

The Council refers to this as being a "demon portal," one who can be forced to channel the essence of a demon through their consciousness. (This may not be the same thing, but something similar.) Colloquially, the process of a ghost being remotely possessed is referred to as "hijacking."

Arthur Wright
Arthur has been hijacked more than once, apparently by unrelated demons. The first few times this occurred were used the same way: as a means of terrorizing someone with an act of sexual assault. The reason for this exact method is unknown, as Arthur has no history of sex-related violence. More than likely, this is because demons derive power from such acts, and the added suffering and fear only magnifies that gain. Both times, Arthur remained aware but unable to prevent his actions, beyond giving a warning that he was not in control.

Subsequent acts of hijacking saw him used more violently and with less and less awareness. The most recent one, he was not aware at all, comparing the handful of moments he was hijacked to "blacking out" and waking up somewhere else. This implies the level of awareness may vary based on the level of control the demon has on the ghost, or the distance between them (the puppeteer was probably closer the latest time than any other time).

He had displayed no ability to fight off this control on his own.