Similar to the Light-Killing Barrier, an Eclipse Field is a type of barrier which prevents any shape of intervention being performed, meaning that anyone inside the barrier cannot interact with any being outside of it, and vice versa. In order for the field to actually be formed, Tager is required to use all of his systems, meaning that, since Tager is a Event Weapon Imitation, a extortionate amount of power has to be used for it to be generated.
In BlazBlue: Chronophantasma, the Eclipse Field was used primarily to prevent Tsubaki Yayoi from escaping Makoto Nanaya, Noel Vermillion and Jin Kisaragi inside the Colosseum after the Battle of Ragna the Bloodedge. The use of the field confirmed Tsubaki’s suspicions that Kagura Mutsuki was planning a coup d'état against the Emperor. Eventually, after Noel, Makoto and Jin finally broke Tsubaki out of the Emperor’s Mind Eater, the field was lowered.