Rare Weapon (Greataxe), Heavy, Two-Handed, Requires Attunement 

Forked Lightning. The first time you hit a creature with this magical weapon during each turn, two forked lightning emerge from the blades of the weapon, each forming a line 25 feet long and 5 feet wide. Each creature in the line must make a DC 13 Dexterity saving throw, taking 1d6 lightning damage on a failure.
The lightnings blast out from the hit creature in two opposite directions perpendicular to your position. 

Overcharged Strike (Recharge 5-6). You charge your weapon with the power of lightning, your next successful melee attack with this weapon causes a lightning blast with a 15-feet radius area. Each creature caught in the area must make a DC 13 Dexterity saving throw, taking 1d12 Lightning Damage on a failure. The hit creature has disadvantage on the saving throw.
When you use this feature, your next Forked Lightning deals additional 1d6 Lightning damage.