You will go to the mid lane and just creeping and harrashing with your Q, play safe as possible as you can till the just level 2. After you open your Shunpo (your base power E skill) start the harrashing hard, jump to the opponent with your E then send him a Q than go back, im %100 sure he cant think to attack you cuz your harrasment will be too hard and he will run away from you. Do it again and again (but dont forget always play safe and look at map for ss kata gets damage hard too). Even you dont kill your opponent at mid im %100 sure again he will go to the base at least, that means you will be 6 before him and open your ulti. Now you have to do just one thing buy your magic penetration shoes at least then you can do whatever you want. if you want go and kill your mid opponent first then go to the top or bot for gank someone,im pretty sure you can get one kill at least. After this time no-one can hold you if you play smart. Take care of you, and my Kata :)

Something about team work.. Do early ganks with your OP champ to help your teammates and improve yourself.. And dont forget it, Kata gets damages too hard, at teamfights always stay back and wait for true moment, when the chaos begins (maybe some enemy stuns used) jump with your shunpo to the crowd and open your ulti, Kill em all !

Dont ask me that why dont you use Hextech Gunblade please. I tried it too but its my build and im always getting excellent results with that build. If you want to spend money too much, i say buy another rabaddon to you and see your damage :) But after all, if you want to buy Hextech Gunblade you can buy it for your sixth item and use active like exhaust.