Realms are locally real spatial groups. The physics of each realm is self-contained and not bound by universal laws. Realms can be created or destroyed, but the energy within realms is always preserved. Realms are categorized by sets.
Grand Realm
The Grand Realm is the set of all Realms that contain themselves and are not contained in another realm. Realms within this set are known as universe realms.
Materia
Materia is a universe realm that contains our known universe.
Tartaria
Tartaria is a universe realm that contains all abyssal realms, such as Hell and Makai.
Celestia
Celestia is a universe realm that contains all celestial realms, such as Heaven.
Subrealms
Subrealms are defined as the set of all realms that contain themselves and are contained by another realm.
Hidden Realms
Hidden realms are subrealms that defy local physics. Such realms may exist with the spacetime of another realm, but appear to have no measurable effect on the realm apart from Vymar-Real waves. Until 2025, Gensokyo and The Lunatic Kingdom were hidden realms.
Subspace
Subspace is the set of all realms that do not contain themselves.