This Combo in Guilty Gear Xrd -SIGN- is Horse Shit

I have been trying literally for hours to pull off challenge 21 for Sol Badguy in Guilty Gear Xrd -SIGN- (great name, I know).  How do people do this?

How?  How am I supposed to do that?  Christ.  It’s not that I’m so uncoordinated.  I can do this. Someone help.