I don't think I have a particular comic rival for Grassblades, no. I mean, I get sudden stings of jealousy, yes, but that's mostly for other artists in general and their mad skillz or cool jobs, not because their work is particularly similar to mine.
Grassblades is already consciously inspired by a good number of established tropes (as seen in Lone Wolf and Cub, Blade of the Immortal, etc.), so I was kind of aware of that going in. Up until now, I haven't really found anything that makes me feel haunted in that way, I guess?
I do have a BUNCH of anxieties about my work, but they're pretty non-specific. Just this.... amorphous cloud of fear that occasionally forces me to unplug my computer and go play Spyro the Dragon and eat cookies until I feel better. >.<