Due to his natural reset nature, Kha'Zix makes great use of Dark Harvest's perpetual damage increase upon killing enemy champions.
Through the use of his [R] and [E] Kha'Zix is able to keep Sudden Impact's Lethality buff for the entirety of almost all fights.
Kill wards, kills champion, gain damage. Kha loves to check all of those boxes so Eyeball Collection is a no-brainer.
Ingenious Hunter provides an incredible amount of item CDR. A few early kills and you'll be clearing every ward with Duskblade and entering every lane with Ghostblade.
WhyCoup De Grace
Execution on squishy targets is the name of the game for Kha'Zix so Coup De Grace adds the most damage for ending those target's lives ASAP.
Because you're naturally looking to kill ASAP, reset, and jump to the next target you'll want to make sure you're healthy enough to move on and Triumph plays up on that by giving you a lot of health after each kill.