The Fusion Edge was originally developed as a cutting and welding tool, and was later weaponized.
|“||A fusion edge, here shown extinguished and without its amplifier pack. In the hands of a skilled pilot, it is the deadliest weapon in the mobile frame arsenal. Unlike a projectile or beam weapon, its precise use minimizes threat to friendlies, civilians, or infrastructure.||”|
–Mobile Frame Zero: Rapid Attack rulebook , pg. 33
The cutting "blade" of the fusion edge is plasma constrained by a magnetic field, that is shaped by a core. A fusion edge can be blocked by another fusion edge or a magnetically charged shield.
Fusion Edges require frames with large power supplies, limiting their use.
Main Source: Mobile Frame Zero: Rapid Attack Rulebook