EXS

The Manifestation, EXS(Exist) (顕現(イグジス)) is the source of an In-Birth's power and what Voids seek to consume. It is a form of energy present in all earthly matter, described as "the source of all things".

Exist (EXS)

In-Births are capable of using the power of Manifestation to give the EXS stored within their Vessel a unique form of their own, this form is known as an EXS ability; In-Births that possess EXS also have their physical abilities enhanced to a degree, as elaborated by Tsurugi and demonstrated by Chaos, which is likely enough for them to at least manage their powers.

Overuse of EXS abilities or gathering large amounts of EXS within one's Vessel however, can cause an In-Birth to lose themselves and start having their true self replaced by some sort of "alternate self". This alternate self starts to emerge in personality traits such as an increased bloodlust or fits of rage. Soon, these traits completely overwhelm an In-Birth and they begin to transform into a Void, a creature that is driven by instinct to consume EXS and can manifest itself in the presence of large concentrations of it if they are powerful enough.

The Abyss at the center of the Hollow Night produces an endless amount of EXS, attracting Voids as well as In-Births seeking to gain further power, and possibly even the status of a Re-Birth if that's what they so desire.

It would also appear, based on story dialogue, that characters from other universes such as Eltnum and Akatsuki do not require EXS to use their abilities, though they still contain it within their being and are thus, vulnerable to consumption by Voids.

If an In-Birth does not use their abilities for a certain amount of time, their abilities will eventually vanish, turning them back into a regular human.

False (FLS)

The FLS(False) (虚偽(ファルス)) is a power used by Voids and Autonomic Nerves to fuel their abilities. In order to use FLS, a Curse Commandment is required.

Currently, Merkava and Vatista are the only playable characters to make use of FLS rather than EXS. Kuu is also known to use FLS due to his status as a Void.