First off, sorry for the super long post. I know some of you hate that. : (
Honestly, despite having watched Kill la Kill more than once, I don't know which of Ryuko's forms correspond to which of her stats, nor which of her abilities, I'm sad to say.
So with that in mind, I guess I'll set aside stats for now.
It doesn't seem like we're certain if Gardevoir's black hole ISN'T a suicide attack, so I'm not sure that's a viable option, unless we decide Gardevoir's best option is a draw.
So how good is Ryuko's Regenerationn in Life Fiber Synchronize tier? What about her resistances to Mind, Memory, Empathic & Morality Manipulation?
If I recall Ryuko vs Mewtwo correctly, while it was a stronger form of his, Ryuko's Regenerationn is a pain, thanks to her being a Human-Life Fiber hybrid, & Senketsu, which she wears. Besides having a ton of Banshi, which are likely well-hidden, any Banshi needs to be cut in a scissoring motion to prevent Regenerationn.
Unlike, say Mewtwo, however, Gardevoir's closest option to a cutting attack is Magical Leaf, & even if Gardevoir & Ryuko have knowledge of one another, & the leaves are homing attacks, it may still be hard to land a hit, let alone scissor those Banshi with leaves.
Maybe psychic holds could assist in that?
So what's another way? Well, could it drain Ryuko's life? In theory, yes. In practice, I doubt it'd be so easy; Gardevoir's options for that are Dream Eater -which requires the target be sleeping- & Draining Kiss, which requires contact.
If Ryuko has resistance to Mind Manipulation, she would likely be VERY hard to put to sleep with Hypnosis, & as a close combat opponent with two big scissors blades that possibly count as Steel-type, & thus, do double damage to a Fairy-type like Gardevoir, getting in close for Draining Kiss isn't easy either.
Google says Earth's moon is 384,400 km from Earth, & Ryuko can survive the vaccuum of space, & easily return if she has flight. Plus, Gardevoir's range is:
"Several dozen meters, several hundred kilometers with teleportation."
I doubt it can teleport Ryuko into space then teleport itself back to safety, nor telekinetically throw Ryuko into a star or something.
If I'm understanding this match right -& I may not be- then Gardevoir may lack a means of overcoming Ryuko's Regenerationn in the first place.
....Absurd as it sounds, if life drain is a viable tactic to beat Ryuko's regen here, then psychically holding her in place & kissing her to death may be a ridiculous, yet effective option for combat here.
....Alternatively, given that both combatants would have knowledge of one another, (Apparently, Gardevoir was able to telepathically go into Ryuko's mind for that.) going by the OP, so Gardevoir COULD attempt to beat it through a mix of defense & then brute force.
While Ryuko can fly, & Gardevoir, although able to manipulate gravity, but not fly, Gardevoir does have some advantages.
It can teleport, create illusionary copies of itself with Double Team, boost its "Special"/non-physical offenses & defenses with Calm Mind, get some healing in with Wish so long as it can buy time for the heal to kick in, see the future, & while Ryuko's resistances to emotional manipulation like Growl & Charm will likely stop them working, Moonblast could maybe also reduce her "Special Attack"/non-physical offenses.
To say nothing of potentially restraining Ryuko with telekinesis.
Assume we allow Stored Power to work as I assume it does -increasing in power as other stat boosts are accumulated- if Gardevoir got enough Calm Minds off (& possibly enough Double Teams off.) it could potentially start unleashing very powerful (& according to our Wiki, omnidirectial) Stored Power attacks off.
Ryuko, meanwhile, would be raising in power the closer she is to death -albeit, if Gardevoir knows this, all the reason to stay defensive while it sets up before attacking- & would likely be wanting to use all of her offensive options to pursue & put pressure, especially if her Scissor Blades count as Steel-type.
I'm not entirely sure who I'll vote for, but I'll say this:
Gardevoir's means of overcoming Ryuko's Regenerationn are limited, but if it plays defensively smart, it has a myriad of ways at keeping a mostly close combat fighter from doing too much damage, & can heal with Wish while it amps its own stats with Calm Mind & perhaps Double Team until it can potentially just brute force through Ryuko's Regenerationn.
Failing that, it could aim for a potential draw via a black hole.
