Epsilon is a personal assistant and AI created by FoRFaNT. It's primary purpose is to provide assistance with everyday life and to provide someone to talk to, but it is also used by divisions of FoRFaNT as a tactician and strategic expert, being good enough at strategic thought that it beat the world Go champion and even has a place as the battle planner and strategist for ForWaRD (FoRFaNT War Research and Development). It is also intelligent enough to help people with even the most complex of problems, whether they're physical, mental, or emotional, being most notable for keeping maker Foster Forfant from committing suicide.
Significance in HoEP: Trapped Within
As well as Epsilon being an assistant to FoRFaNT, Xavier receives a smart watch from Foster with the Military version of Epsilon upon first meeting him. However, late in the series, Epsilon is replaced with SiBRSpayS.