Kukata is a practice among the Venerable to punish acts of extreme dishonor. Since the Venerable cannot breed true since The Wombplague, infants born of them never being present in the Loomand therefore unable to naturally weave themselves into it, they have the strings of the soul knotted to a phylactery so that when they die, their soul can be recycled into the next generation.
Kukata is the act of severing this bond with a criminal’s phylactery, to essentially punish acts of extreme dishonor by removing someone from cycle of rebirth. Their soul, upon death, does not even re-enter the Loom, as what happens with most creatures. Instead, it dissolves away as a Wisp, to be used as a source of fuel by some anagogic sorcerers.
Kukata is administered, in lieu of execution, in order to give the sentenced a chance at redemption. It is a punishment almost solely reserved for those of high social standing or with exceptional talents which may be useful to the empire. Very few actually receive forgiveness, but those who do are allowed to be knotted back to their phylactery in the Nascent Keep.
Another reason for a kukata is through an action by the Kujeewa, a murder-cult that plagues the roads of Thassal and Zapandi. It is unknown where members of the cult learned to perform the complicated act of Tuning needed to perform the ritual, but it is known that they are responsible for removing thousands of Venerable from the cycle of rebirth.