Path of the Storm Giant

Barbarians who walk the Path of the Storm Giant draw strength from the primal forces that are the Giants and their elemental ilk. Their rages surge with elemental power and cause these barbarians to grow in size, transforming them into avatars of primordial might. During their rage, a barbarian take after a legendary storm giant, hair turning white and eyes crackling with lightning.

Power of the Storm

By Invoking "Power of the Storm", the Barbarian is now able to cast specific spells while raging. 
At 3rd level you now have the ability to cast the following cantrips while Raging.
Booming Blade, Shocking Grasp, Lightning Lure, and Thunderclap. (You may add your Rage bonus to the damage of these spells once per turn.)

You also learn Thunderous Smite at 1st level, and may cast it a number of times equal to your proficiency bonus per long rest. (Every 3 additional Barbarian Levels this spell can be cast one level higher.)

In addition, While raging you have resistance to Thunder and Lightning damage. 

Primordial Rage of the Storm

At 6th level, your bond with the elemental might of giants and their ilk grows, and you learn to infuse weapons and yourself with primordial energy, gaining the following benefits.

Elemental Cleaver. When you enter your rage, you can infuse one weapon of your choice that you are holding with one of the following damage types: Thunder or Lightning. While you wield the infused weapon during your rage, the weapon’s damage type changes to the chosen type and it deals an extra 1d6 damage of the chosen type when it hits. 

While raging and holding the infused weapon, you can use a bonus action to change the infused weapon’s current damage type to a different one from the above damage types.

Giant Stature. When you enter Rage you can choose to become a size Large creature as if you were under the effect of the Enlarge Spell. In addition to the other effects of Enlarge your Reach is increased by 5 feet as well.

Aura of the Storm Giants

Beginning at 10th level, your connection to Storm Giants grants you the ability to effect the very air around you. You gain a 15 foot Aura empowered by the Storm. 

All allies in your Aura Including yourself Gain one level of Lightning and Thunder Resistance. (Absorb>Immune>Resistant>Base>Venerable) 

All hostel creatures in your Aura lose one level of Lightning and Thunder Resistance. (Absorb>Immune>Resistant>Base>Venerable) 

Colossus Storm Giant

At 14th level, the primordial power of your rage intensifies.

When you rage and use your Giant Stature ability your can increase to Huge size now and your reach is increased by 10 feet. In addition, the extra damage dealt by your Elemental Cleaver feature increases by 2d6.