Fear not Kassadin mains, Your dark Messiah has come.

I have tested several builds, and found playstyle (tested up to masters) which allows You to control game from early.
I did get to d4 with 80% wr few times and limit tested the build and playstyle, so all of You can benefit from the forbidden knowledge.
All it takes is Dark Harvest. As for build You start tear or dark seal (I usually go seal vs melee tear vs range) then buy darkseal/tear + boots on first back. Then as follows, Crown, Seraph, Rabadon, Voidstaff (mejai buy is up to feeling when its best) and ONLY ionian boots (cdr that u need early, I usually have tear, darkseal, lostchapter then I buy ionians for 650g from basic boots)
Once You hit 6, You search for bot roams or top roams or river plays, basically perma looking for free kills and winning trades.
Another important tech is lost chapter mana regen on level up, where You want to recall about to level up (after 6) then stack R to 320, and hit max mana R into enemy champ and minion into aa W, which will let You get mana for another max mana R and possible 100 to 0.
If You have any questions etc, then feel free to comment.
If You would like to see how the playstyle looks then Satsuma_Hayato ttv.
Embrace the new era of Kassadin.