Metaphysics, in the context of plurality refers to the collection of spiritual beliefs surrounding tulpas, and other forms of plurality. A person who is "metaphysical" is a person who thinks about tulpas or similar from a spiritual or religious perspective, as opposed to those who think about it from a "physicalist" or science-only perspective.
The tulpamancy community is by and large the least metaphysical of the active plural communities. However, every community has spiritual members and every community has non-spiritual members.
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The esoteric religion of Chaos Magick is one of the only religions to directly reference the phenomenon of tulpas. Within this belief system, tulpas are internal, or constructed spirits, in contrast to external spirits, who visit the wizard from outside. Tulpas are part of a family of constructed spirits, and they have several hypothetical spiritual abilities. They can hop between persons, possibly to torment an enemy or aid a friend. They can rebel against the wizard, they can collect information from the astral, and enhance the wizard's cognitive abilities.
Tulpas are respected as free agents, but are seen as tools, and are thus only created with care, and kept secure through the use of protections. This is a major point of disagreement between this belief system and tulpamancers, as tulpas have a very strong voice in the tulpamancy community.
Walk-ins exist. However, they are very surprising. The seem to just appear in a head, fully formed, and ready for action. This challenges basic tulpamancy theory, and also basic theory of traumagenic plurality, which suggest that you have to put great effort into creating a tulpa, or a great traumatic event must cause them. Though both of these ideas are contested, there is another solution as well. Walk-ins are almost universally interpreted as external spirits, or spirits that came from outside, and are visiting you.
They often have bold personalities, and are quite unpredictable early on. Walk-ins also frequently walk out, or disappear suddenly. Lacking a spiritual explanation, events such as this have the disturbing implication that the person ceased to exist. However, it is obvious that the walk-in has simply moved on to a new domain from a spiritual perspective.