The pentacle in Onmyoudou is called the Gobosei. The Gobosei is like a Shinto mirror, allowing Gods, Kami, spirits, and Shikigami to manifest into the physical planes through various forms. The Gobosei is also able to reflect back like a mirror meaning it is able to reflect spirit back into the astral or spiritual plane (banishment). When the Gobosei is used in a ritual it may also be used as a magick circle. This magick circle invokes the Wu Xing for protection and containment of spirit; very similar to the Western method of the pentacle. Conjuring spirits is another aspect of the pentacle;e or Gobosei to be used in ritual and magick. The following are examples of rituals used with the Gobosei to cause manifestation, banishment, and circle casting as well as conjuration.
Example one: Manifestation. Using the Gobosei to plainly manifest spirit and the will of entities into this world is rather challenging due to the nature of the Gobosei. The nature of the Gobosei is that it requires the spirit of the caster (the energy of the caster) to charge and empower the Gobosei for the intent of Manifestation. As well as that there must be a spirit already aware of the ritual and ready to aid and manifest. This act of manifestation also requires tools as well. The Gobosei is a spell and not an all-powerful symbol. All spells require energy, power, and intent like any other tool in the occult.
Example Two: Banishment. The Gobosei as stated before is not "God" or a creator of miracles. It can only manifest what it has and only banish what it has as well, meaning that is there is no natural or change the related way to banish something it can't be done.
Example Three: Circle casting using the Wu Xing. circle casting works like any other method of casting a circle. it draws the forces needed to protect and contain the spirit or energy inside the spell or working. The Gobosei must be charged then command with intent to invoke the Wu Xing.
Example Four: Conjuration. Using the charged energies of the Gobosei the caster is able to conjure spirits. therefore not from nothing though. Using the tools around the caster and the Gobosei both the pentacle and caster are able to create or "make" spirits from elemental forces already present.
Again that is the end of my lecture and I hope You enjoyed feel free to comment at any time as long as it is helpful to yourself and others around you.