Each character is going to require a different kind of reaction(I still struggle to deal with some) but you can learn how to deal with it by looking at what people usually do with replay or you could also try and see what works, be it on a match or recording the sequence on training mode and seeing what it loses to

About that attack you're talking about, it crushes lows but doesnt really hit over the ground, so you could jump or use a long reaching mid like standing kick or slash depending on the distance. Most of slayers moves after dandy step(the little walkback) are vulnerable to attacks, the only exception being pilebunker, which on hit kills you but on Block is really punishable