I agree, akali should never be build as an auto attack champion. However she does do physical damage. This item when fully stacked adds 100 damage to her burst each time, and 25% lifesteal. It does add survivability, but now that I think about it, it's probably not the best last item... I'll probably change that soon.

Lost as to why you build a bloodthirster...Akali is most certainly NOT an autoattack champion, and that last slot could be used much more towards your benefit, especially in terms of survivability. Also I suggest removing two of the Attack Damage reds for Magic Pen, mainly because with your current setup you only need 7 of them to activate your passive. You won't really see that much of a change, but it definitely helps.

Also, I've never made a guide before, so I'm sorry if it's boring or unorganized!