Soul

Soul (魂) refers to the spiritual being of a life-form. The Soul is the core of every entity, there is no "being" any deeper than it, it is the very concept of every individual. By itself, it's extremely fragile and usually requires a three-fold Body to be able to operate normally.

Reincarnated individuals from otherworlds that survived the crossing of worlds bear a strong soul, allowing them to most likely acquire powerful abilities, sometimes including a Unique Skill.

Ego
The Ego (自我) is the "being" of an individual, and their sense of self. It's the only part of a soul, when removed from its makeup, results in insanity. A being without an ego cannot access Skills. The ego is described to be a set of amorphous wavelengths. Surrounded by a group of information particles, this construct is known as the Nucleic Heart. Reincarnators usually lose most of their ego, but sometimes strong souls, like Satoru Mikami, can retain their ego despite the dimensional travel.

Nucleic Heart
The Nucleic Heart or Heart Core (心核) is the core of the soul, where the most powerful of Skills tend to be stored. It is not possible to remove Skills that are engraved here, though Mammon, Lord of Greed, can remove it under certain conditions.

Astral Body
The container for the soul and the form of a being. This layer requires a medium to preserve it, with it otherwise slowly dissolving back to Magicules in the surrounding space, releasing the ego and nucleic heart and allowing for reincarnation. That medium is usually the Material Body but it can temporarily be the Spiritual Body. Those with the power to solidify their spiritual bodies can maintain their existence indefinitely.

Name
A Name can be inscribed into a soul completing it and making it stronger. Named beings typically have much stronger wills as well as more diverse and complex emotions.

Soul Connection
A Soul Connection can be formed by various means with different strengths. Equal naming will result in a weak bond while subordinate naming will result in a stronger bond. A bond can even be created through a strong belief.

Soul Corridor
The Soul Corridor (魂の回廊) is the strongest soul connection one can have with someone. A significant enough relation and certain conditions are required for a soul corridor to form. Communication carried out via this link transcends time and space, and cannot be picked up on by third parties unlike with other means of communication. The emotions of the speaker can be more keenly felt through this link than otherwise.

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