The passive is currently still not activated with your rune. With 9 Greater Mark of Attack Damage you need at least 1 point in Brute Force . Alternatively I could suggest going 8 Greater Mark of Attack Damage and 2 point in Brute Force or 7 Greater Mark of Attack Damage and 3 point in Brute Force . The left over rune spots in marks could be used Greater Mark of Magic Penetration or the new hybrid rune.

Thanks for the comment/suggestion,marks of potency has been changed to marks of might to activate spell vamp passive :)

i honestly dont think you need that many flat AP runes... you only need to get flat ap runes so you can get 19.5 AP to activate your Twin Disciplines passive. Once you get 19.5 AP from runes and masteries, the remaining runes should go into ap per level runes to maximise your damage output.

It might seem like a nice idea tog et flat ap runes to have a strong harassment prior to level 6 but trust me, Akali can't harass as well as other champs prior to level 6. Once she hits level 6, she becomes a threat because of her Shadow Dance. You only need to land one Mark of the Assassin and the enemy champion should back off a bit as they will fear the combo about to come. For that very reason i recommend getting ap per level runes.

No where do I see in your item build, masteries or rune that you attempt to activate the second passive of Twin Disciplines. Trust me the spell vamp passive is really useful! It allows your to harass and steal heal some damage as well as bursting in but minimising damage received cause of the spell vamp.