The only use is for Hybrid attackers, which are few and between, but imo, suck, since even the sterner stuff like eiki would bank on Last Judgment in the late over Bar of the Ten Kings.
Well, when you say Hybrid attackers, I'd assume something more in the composite attack category. But, since Reimu should be defensive, the best composite attacker is Ran herself, and the only other notable one that comes to mind is Orin, that's not really a problem.
IMO since Ran's buffs take soooo long to build up, and I tend to have Iku out almost 24/7 once I'm a good bit into the game, (And I've tried using Keine as a backup+Offtank, worked pretty great), a better use for her IMO (At least in my setups) is being an amazing attacker or a defensive buffer; keep dem DEF/MND buffs from wearing off by using it every turn, and people just switching in are already all walled up :] Also, if you aren't doing Winner by having Ran use her DEF/MND buff every single turn to keep your entire team constantly at 80~100% buffs, you're doing it wrong and just making it harder on yourself. Seriously. Also likely applies to Hibachi Twins. DEF-Based Ran is a wonderful tank too, by the way, better in all stats then my DEF-Based Yukari that I used wonderfully the entire game.
And yes, Ran has just about the best composite damage considering her formula ((350% of each wheras the next best from Reimu/Orin are 400%, but Ran has higher stat growths albiet a little slower leveling)), and THEEEN she ALSO has better survivability AND oh my god 70% delay that is just godly, only 70. Percent. Delay. That's Aya-tier right there, even if she isn't quite as fast as Aya (still fastish though).
oh goodness ranting is fun
anyway Keine is great as a back up for Iku, a version with higher speed to actually buff up attackers before they attack in randoms, and as a tanky gal, but she definitely doesn't -replace- Iku and isn't hugely needed, which is why I dropped her after awhile