I think when you do j.C you're supposed to have some momentum that lets you slide as you do 5A > 5C, but I couldn't figure out how to get the momentum.
I also did it in the corner =P
what i do is when rachel does her cannon, i react by doing 3c for a free combo. i sometimes run in for a grab so that the rachel cant use her electric chair on me
i usually dash in and do 2b 3b to pressure him. and when im dashing in and hakumen does his really annoying poke, i do 3c and if im lucky, i can get a free combo off of it