Story & World
Semiplane
A small, temporary Plane spun up from both fighters' Anima Aspect energy when a Nexus Battle begins; it dissipates when the battle ends.
A Semiplane is a small, temporary Plane that forms when a Nexus Battle begins, spun up from the Aspect energy of both fighters' Anima. When the battle ends, it dissipates.
It's how the battle system fits into the lore: after the Sundering, Nexus Battles became the accepted way to settle disputes, and each one conjures its own Semiplane to be fought in.