I like the idea! I can see her with Energy... But, don't Ninjas have Energy?

I mean, I don't think Lee Sin is but the question still stands.
Also, I want to share my old idea of a Riven ability cost/passive
(It's rough as I forgot about it; talked about it a long time ago)
I am stealing the concepts from other champions as I don't have time to remember exactly what wording I used.
Giving her a similar Passive to Rumble's Junkyard Titan:
Using abilites will give her Heat, or 'Exile' if you will.
Basic Passive: Riven's blade gains a charge for 4 seconds every time she casts an ability. Each of her basic attacks consumes an available charge to deal bonus physical damage.
Ability Passive: Riven gains 5 Exile every time she uses a basic ability, and loses 10 Exile per second after 1 seconds of not using her abilities, of 100. (Roughly)
Half: Riven's ability cooldowns are reduced by 25% at 50 Exile or above.
Max: At 100 Exile, Riven slows herself for 6 seconds, which he cannot mitigate or cancel by any means, but her abilities are reduced by 90% and for each basic attack she deals she causes enemies to bleed for the duration, during which her Exile also decays back to 0.
What is broken can be reforged.
##Don't attack me if this doesn't tickle your fancy. It doesn't have to happen, I just thought it was a good idea, too.