Bio-Em

The ability to use Bio-Electromagnetic (Bio-EM) fields for communication brings us into a realm that is part science, part high fantasy. To construct a scenario where two spiritually attuned individuals could communicate through their metaphysical auras, we need to bend the rules of our known world just a bit. The following explanation will combine elements of real science with fantastical elements typical of high fantasy literature.
Every living being emits a Bio-EM field - a natural aura. This energy field is a consequence of the biological processes that take place within the body, such as the electrical activity of the nervous system and the magnetic field produced by the flow of blood. For most beings, this aura is a mere byproduct of life. However, for a select few, it's a means of communication.
These individuals, often known as "Aurics" or "Aura Translators," are born with a rare ability. They can consciously perceive and manipulate their own Bio-EM fields. With training and concentration, they can cause fluctuations in their auras that mirror their thoughts and emotions. Not only that, but they can also perceive the Bio-EM fields of others, allowing them to "read" these aura messages.
To communicate, the Aurics need to enter a meditative state, focusing their mind on the message they wish to send. This message would then be translated into a pattern of Bio-EM fluctuations in their aura. These fluctuations could then be "broadcasted" over a certain distance. The receiving Auric would sense these changes in their own aura, and through their unique ability, they'd translate the Bio-EM fluctuations back into a comprehensible message.
This form of communication would be highly secure, as only those capable of manipulating and perceiving auras could participate. Also, since it would depend on Bio-EM fields, it wouldn't be hindered by physical barriers like walls or even mountains. However, the distance over which this communication could occur might be limited, and the process would likely require a significant amount of energy and concentration.
This form of silent communication combines elements of electromagnetic biology with spiritual concepts. It provides a plausible (in a high fantasy context) method for two individuals to silently communicate using nothing but their innate abilities and the natural energies produced by their bodies.