Darius & Vi Synergy
Darius Top and Vi Jungle win 46.9% of 2,790 Low Elo games together, -0.2 points vs expected, 2-patch window 26.19-26.20.
Researched on LoL patch 26.20. Tips are written to hold at any rank; stats come from Low Elo ranked games up to patch 26.20.
Playing the duo
Vi's Cease and Desist(R) knocks its target into the air, and Darius' Hemorrhage(P) takes repeated hits to stack; Darius players say chained jungle crowd control helps him reach the five stacks that increase Noxian Guillotine(R)'s damage.
How to play as Darius
When you are close enough to follow Vi's Cease and Desist(R), use Apprehend(E) or Crippling Strike(W) to keep building Hemorrhage(P) stacks, then use Noxian Guillotine(R) once the stacks are high; your damage rises sharply at five.
How to play as Vi
Signal your top gank early, then use Cease and Desist(R) when Darius can follow; the knockup gives him a chance to chain Apprehend(E) and build Hemorrhage(P) stacks.
Sources
These notes come from r/Dariusmains, checked against the champions' abilities.