I've been playing Darius for a while now, and decided to try a new build, and surprisingly it works.
It works like thus;

. Darius's passive deals a high amount of magic damage, especially early game.
. Darius's ult refreshes on kill, so you can use dfg and BoRK to burst them down for a dunk, and especially after the nerfs to his ult reset, you can rely on your magic pen to let your passive finish them in small skirmishes where the reset isn't needed, and your passive with Liandry's for that extra damage in teamfights.
. The spellvamp from Spectral Wraith gives you the normal tankiness you would get in a teamfight from a normal Darius build.
. Darius doesn't scale terribly well with AD.

Pros:

. Really high early-level damage, due to the magic pen and your passive along with Darius's high base ability damage
. Really high damage in extended fights
. It's Darius, everyone loves to dunk, even better when you can one shot squishies

I'm not going to list what his abilities do here, as if you don't know you can check where the skill order is by hovering over them.


Hemorrhage (Passive)

The main source of damage in this build, it does surprising amounts, especially early, and even more so as people will build armour, and not magic resist versus you

Decimate (Q)

A nice chunk of damage, even at level one, as we max it last in this build. As I said above, our main source of damage, especially early, is our passive, not our Q