BlazBlue: Continuum Shift

She's the last opponent in score attack mode

An easy way to beat her is to pick Tager in beginner mode.
At the beginning of the fight, go in the left corner and block everything she drops you untill she comes close to you, when she is, tap C (B button on xbox controller)
to perform the big chop, when you both come back to the ground, spam C,
with this move Tager grab rachel from the ground and replace her on her feet.
Now coninue to spam C to grab her again and do the big chop one more time. then repeat the sequence again and again.

Doing this way you can easily perform your big chop 2 or 3 times in a raw
When, you see she's low on health (nearly 25 or 30%),
you can do your distorsion move by holding A
(X button on xbox controller) right after you replace her on her feet

For sure this method is a bit based on luck cause Rachel is a very tuff opponent and drops you a lot of craps that can break your spam sequence

But it's really harder to try to fight her normally,
personnally doing this way i beat her in 2 tries
Hope this helps

you will get this after defeating the last enemy in score attack, rachel in her unlimited form. put out your strongest attacks to defeat her. she gets crazy and beasty when she gets into low health. if you feel you will lose the fight just push start on your second controller to fight against him so you can get another chance to defeat her. good luck and be patienced