Reiatsu

Skip these chapters, they are introduced later in the story.

The amount of reiatsu a being possessed was categorised into 5 levels: Basic, Average, High, Great and Immense.

Basic amount of reiatsu is the common level of power of a regular human as they possess the bare minimum (Below average Class).

Average amount of reiatsu is the common level of power among non-seated and low ranked seated officers (Average Class).

High amount of reiatsu is the common level of power among high ranked seated and average lieutenant ranked officers (Lieutenant Class).

Great amount of reiatsu is the common level of power amongst those of an average captain rank. (Captain Class)

Lastly, Immense amount of Reiatsu. This level of spiritual power is reflected in its ability to enhance a user during combat as well as its ability to affect the surrounding environment on a controlled level, allowing the wielder to use it in combat to startling degrees (Advanced Captain-Class).

They are then categorised into Upper and Lower.

Furthermore, they can also be categorised into 'Orderly' and 'Chaotic' which corresponds to how well the Shinigami can control his Reiatsu. Orderly being very well controlled and chaotic being having no control at all.