Yeah, like suna said, you can sweep it with most character's sweeps. You asked about how to punish on block, not how to stop a bad Mitsuru from spamming it mindlessly. That said, you're not playing the matchup right if you're getting hit by that all the time or even blocking it... you're much faster than her. You should be able to run circles around most Mitsuru players without being in danger of getting hit. Just be careful of a DP if you ever try a crossover.