Gunblade Akali

That's her powerspike item. Like ADCs power spike at 3 items or so. Like old Fiora used to power spike at Hydra. Like Irelia hits her power spike at trinity force. For Akali, its Gunblade.

Its the most efficient item on her, providing hybrid stats for her needs.

Hextech Gunblade can be considered the highest amount of offensive stats packed into one item in the game. If a champion can make use of its hybrid stats, e.g. Akali, Mordekaiser, Jax, Ezreal, then they can rush the item to use as a power spike. This particular spike is powerful because, say an opponent was winning the lane facing one of these champions when they only had Cutlass and Revolver. Upon completion of the item, they get 15 AD, 40 AP, and a 250 (30%AP) active to suddenly overwhelm their opponent with a sudden increase in power. The omnivamp also helps in out-trades.

I was in an aram where the Akali built gunblade and then went tank

She still became her team and won the game for them...

With 1 damage item...she's healing everything and doing lots of damage, I don't get it..

i know right she can literaly q and dash and you just got 100 to zero'ed

Still lower than almost nearly every other assassin in the game? As she has a massive deficit in power due to a nearly useless utility spell. The reason it feels like she does a lot is by that point she generally has gotten 3-4 kills and is beginning to snowball. She has more experience and gold than most champs in that game and the gunblade just furthers that gap. That said she is ultimately reliant on gunblade along with the vamp and stats it gives her as otherwise you only are benefitting off of 1 of your dual scalings within your passive.

well, that item was basically designed for her

the item does 300 magic damage with its active. she can kill any squishie after she finishes it. with ease. it doesn't matter what and how. she will force a flash in mid and you might still die.

um its you not building Mr is why your getting REKT. you want her to be garbage the whole game?