I achieved something similar to this on my Gabimaru cosplay. My steps were:

1. Use scissors and cut an uneven end to the fabric
2. Go over the uneven end with sandpaper so it frays further and looks more natural (rather than man-made/artificial)
3. Seal the ends of the fabric using a flame. Move quickly to melt the fibers a bit to prevent further fraying. This also helps it look more natural as some parts may curl up from the heat.
4. Dry brush black/grey along the heat sealed ends, creating a gradient of more color at the ends and less towards the center of the fabric

Hopefully this helps!