Real cool bro. A diversion from you're typical style to the point I'm suprised Riitual thought, "akreon's the guy to do 40k". Let's see more battle scenes from you. You're saying something different in this space than many artists and I want to hear more of it.
I couldn't tell you off the top of my head, and I can't find anything on lexicanum regarding a tau titan-killer, but my best guess would be that the tau don't field one, and instead rely on ambushes and hit-and-run tactics to bring down titans