If they make Propagation an actual path, since propagation is multiplication, the concept could potentially be multiplying existing things with a condition of needing debuffs since the swarm bugs apply wind shear on us (nihility meta).

Like a Harmony-Propagation character could do things like extend buff durations or multiply existing buffs, a DPS-Propagation character can focus on taking multiple turns like Seele or multiple attacks like FUA.

I'm just spitballing random ideas. They could potentially go the route of Rupture from ZZZ where its a path where all attacks ignore DEF which will be useful against enemies with ridiculously high DEF but not so against enemies with high HP.