Glossary

The Score of Spacetime works in conjunction with the Cosmic Law and the Cosmic Scales (Space) and describes the largely unheard "sound" of the Omnicosm, in which each universe has its own "music sheet". The Score largely deals in the course of Time, and thus fate itself. Everyone and everything has their own "personal" Score as well. 

Whereas Ouroboros composed the Score of the Omnicosm and does not conduct its work, Firstborns are able to read, and, to varying extents, orchestrate the Score of Universe A+/A-. Further, whereas Ouroboros hears the entire symphony without discernment, Firstborns can hear each individual instrument, and are thus able to better (not but infallibly) predict their tunes.

Some Firstborns, such as the Composer, can even amend spacetime through the Score (all Firstborns possess a level of spatial skills; temporally, it rarely goes beyond awareness/interpretation of the Score), although their Oath prevents them from unfettered interference.

Notably, fate is far from deterministic; it is a sea of possibilities, and no one action leads anyone or anything on any set path. It is truly a power of will, where the consequences of it simply greaten or lessen the probabilites of each outcome. Some things, of course, are also entirely outside anyone's control, but even they are technically the will of happenstance.