I can’t remember the specific material nodes to do it(Camera Offset I think?), but there’s a way to get a rendering offset working for a particle’s material in UDK that forces the particle to be rendered further back from the camera than their actual location and always rendering them behind the character opposite the camera position.
Here’s a short video I slapped together showing what I mean using a ZEQ2-Lite model of Goku (Because it looked cooler when I messed with auras of that style)…
Works well for the most part, but can look strange by a character’s feet if offset too far(because looking down with the camera will have the particles colliding with the ground a foot or more away), but if you’re careful about how you set it up it can be avoided. Shouldn’t be much different to setup something similar for your needs in UE4.
Generating an “outline” type aura…? That might be possible using a heavily modified version of the Outline/Edge detection Post Processing setup (like the ones used for cel-shading) to create the outline as the aura color you want instead of black, and then just use a series of particle emitters to generate the trail effect. At least, that’s my best guess.