Upon causing an Overloaded, Superconduct, Electro-Charged, or an Electro-infused Swirl reaction, ATK is increased by 20/25/30/35/40% for 12 s.
In Game Description
A perfectly ordinary iron sword, just slightly darker than most.
How to Get Dark Iron Sword?
Obtainable from from Chen the Sharp, street food vendor located next to Wanmin Restaurant in Liyue Harbor, Liyue.
Here’s all material used to upgrade Dark Iron Sword: