Shikkoku was originally used to facilitate the training of younger monks who had yet to sever their ties with the material world and sought guidance from Taizen. It creates an internal strife which one must to overcome; it's a challenging experience to confront the worst aspects of one's self and be triumphant.
This technique requires Taizen to make physical contact with the target, so that he may engrave some of his enlightened wisdom on the soul of the creature he touches. However, this a "double-edged sword".
A creature affected by this ability obtains a newfound awareness of self. As if a veil had been stripped away from its eyes, the creature is able to perceive on a spiritual level their own weaknesses.
The creature can visibly see faint lines, the spiritual manifestation of the creature's personal attachments it has to its own world and things within in it.
For example, a man who lusts after a happily married woman may see his "fetter" as a line that connects he and that woman. However, he will notice that the only a small part of the line is solid and shines brightly, the remainder is faint and darkens as it approaches the object of his lust. Breaking the bond the man has with that woman will release him of his feelings for her, and make it incredibly difficult to forge another link with her.
Shikkoku can help a narcissist to banish his dark thoughts and become more altruistic. It can relieve a grieving widower and grant him or her closure.
Unless they direct link to him, Taizen cannot see these "fetters" nor can he cut them. The affected creature must do this of its own volition. How it can be done varies, but seeking guidance before making any final decisions is strongly recommended.
However, as a result of Taizen's interference, if left unattended, the fetters may become a poison and corrupt the creature even further. This leads to an intense disharmony and severe instability through every level existence. The creature's (physical, mental, and spiritual) health will deteriorate until the fetters have been cut, the ties a creature has to suffering (Dukkha) of any kind.
Desire, anger, hatred, delusion, pride, greed, envy, etc.: the existence of each can be amplified as such aspects are bade to manifest themselves in a more potent manner, if the effects of Shikkoku persist unsupervised.
Any creature that is subjected to Shikkoku's effects and allows the corruption to consume them entirely will die. Upon its death, the creature will become a Hollow.
Shikkoku does not affect Hollows in the same way it does creatures with untainted souls. Because Hollows have lost their heart, the core of their soul and the focal point for all wordly connections
The fetters do not manifest for Hollows because they lack that which connects them to the other and the world.
Instead, Hollows experience an maddening sense of loss, maddeningly tragic, and are overwhelmed with a feeling of tremendous burden. Whether or not their thoughts are coherent, Shikkoku instill within Hollow a longing for completion that temporarily supercedes their insatiable hunger. Because they can no longer determine what their objective or goal in life was, they are truly lost. Shikkoku is a form of spiritual torture for Hollows; forcing them to experience a fragment of the fulfillment they could have had in life torments them.
The common result is this:
The affected Hollow will stumble around in a confused stupor, whining incessantly and bemoaning their pitiable circumstances. They become crippled by a looming uncertainty.
Some become catatonic, while others enter a blind rage and attack their surroundings (and occasionally themselves) indiscriminately. Taizen has observed a few Hollow that actively attempted to destroy themselves, but such cases are exceedingly rare and seem to be confined to the lowest ranks of Hollow.
Interestingly, Taizen has determined that newly turned Hollows can still be saved by using Shikkoku. It is still possible for their "fetters" to manifest, but the lines are very faint and degenerate quickly.