Anji’s impossible dust isn’t about damage but instead about setting up a perfect trap.
There are two ways to do Anji’s impossible dust. You can either use the jump cancel method, or the faultless defense method.
I prefer the FD method so I’ll start with that. Anji’s impossible dust is simple I.D., HS, {land} 623HS.
To do this, after a connected dust you hold up (obviously) as soon as you can, tap two buttons for a faultless defense and then quickly tap HS. Tapping Faultless defense counts as one of your two allowed “jumping actions” so you will fall right after the hard slash connects. After you land quickly do an On, catch them and go from there.
The jump cancel method is the same premise, but instead of Fding, you quickly tap up and jump cancel towards your dusted opponent before you hit HS. They both give the same effect of a connected HS that allows you to fall and catch with an On.
You can follow up the on with an Issen Ougi, or Air combo, but it adds a measly 50 damage at the expense of 50% tension or the loss of your perfect trap setup. Bleh.
Hope that helps.