In a speed equalized this match, this seems surpisingly ambiguous.
Satsuki has advantages in Attack Potency, Striking Strength, & Durability; Where Raikou is "At least Mountain level" in AP & Dura, & "At least Class PJ+" Striking Strength.
Whereas Satsuki is the same in those 3 stats, except for her, each of them has "likely higher".
Going by that alone, I imagine she might have an advantage when it comes to trading blows, & she has "Very high" stamina compared to Raikou's "High" stamina.
Although, the matter of stamina may be influenced by Raikou's Pressure ability. Quoting our page on Raikou:
Pressure: Raikou exerts a pressure on the opponent that makes them expend twice as much energy which tires them out twice as quickly.
Satsuki also has an advantage in being able to fly.
She also does have SOME ranged attacks, such as shockwaves & air slashes. Even if Raikou CAN bring down actual lightning with the move Thunder or the like, Satsuki's speed & flight would likely give her the ability to avoid it, reflexes aside. Although I'm still a little uncertain.
Raikou does have some advantages though. Most notably range, Reflect to weaken physical damage, & if type match-ups apply, it may resist Satsuki's air slashes. Not to mention, her weapon, with its unknown material, may or may not be something it resists, as Electric types resist Steel.
Although, given the vagueness of her Bakuzan's material as a weapon, who knows how much of that applies, not to mention if it's even conductive at all.
Raikou also has Quick Attack, but I'm not sure how that applies in a speed equalized match. Its statistic manipulation in Calm Mind, & the utility of Aura Sphere could also be useful.
Both have High intelligence, so they MAY BE matched tactically. ....Maybe?
Overall, Satsuki has the better offenses, stamina, & durability, if not by a large amount. However, Raikou has the better range, & better hax.
If Raikou keeps its distance, & keeps its defenses up with Reflect, it might be able to manage it with ranged attacks, thanks to the utility of its electric attacks, telekinesis via Extrasensory, the difficult to avoid Aura Sphere, & the offensive & defensive aid of Calm Mind. Its lower stamina may make this difficult, however, especially if it wants to stay out of melee range, considering her higher AP, Dura & SS.
I think I'd like to say Raikou with high difficulty, as long as it uses its hax correctly.