So, after searching through Rachel's profile and thinking, I think X should be able to win if he is careful.
X's main strategy here is to maintain some distance between him and his opponent while also firing shots of energy, and as Rachel uses the environment to try to close the distance, X will try to keep his eyes on her to see where she is going next and avoid incoming attacks.
If Rachel managed to close the gap, X isn't absolutely as helpless as he is made out to be here. X isn't afraid of being in CQC since he has access to his Z-Saber
that he can pull out at any time for an unexpected blow and can use it to parry and deflect Rachel's attacks, while also
being capable of amping up his punches once he gets in close.
X could also jump away from Rachel and either blast/slash her away if she tries to grab him too with her greater LS, since X doesn't seem to be the type to tank attacks and mostly avoids them (Even if she did grab him,
nothing stopping X from cutting her limbs or piercing through her to be released).
By entering his Ultimate Armor, X's injuries will heal up (
Since his injuries instantly recovered after he entered it) as he tries to fly away to gain some distance from the sky to blast her from the air. Rachel could try leaping from tree to tree to get close, but it would likely involve some brief pauses between leaps, and she is still bound by gravity, which doesn't stop X from firing at her while he flies up into the air.
Even if Rachel tries to use her Horn Thrust to sucked him in (Though I am curious what its range is since it isn't really stated in the profile itself), what exactly is stopping X from
using both of his X-Busters to blast her away in order to cancel it?
Plus by firing the Pseudo-Black Hole on the ground, X could just blast one of his charged-up shots of energy at her or ramming into her to knock her off her feet and send her flying for it to consume her as a main finisher,
something that he does attempt before.
Overall, by maintaining some distance from her and using some of his skills to his advantage, I think X wins this mid-diff.