Path of the Weave

As the protector of the Weave, Mystra is a being with monumental magical power. But in sporadic moments, the Weave cannot always be controlled. A barbarian that is introduced to these outbreaks of the Weave often gains immense mystical powers, that instead of conflicting with the raw, unhampered power of a barbarian, it intertwines with fabric of the their rage.

Spellcasting

When you reach 3rd level, you gain the ability to cast spells.

Cantrips. You learn two cantrips of your choice from the abjuration and evocation spell school lists. You learn a an additional cantrip from the abjuration and evocation spell school lists at level 10

Spell Slots. The Path of the Weave uses the same spell list as the Eldritch Knight. To cast a spell, you must expend a a slot of the spell's level or higher. You regain all expended spell when you finish a long rest.

You prepare the list of the abjuration and evocation spell school lists that are available for you to cast, choosing from the any class list. When you do so, choose a number of abjuration and evocation spells equal to your Constitution modifier + your barbarian level (minimum of one spell). The spells must be of a level for which you have spell slots. 

Unlike other classes with prepared spells, you cannot change your prepared spells after a long rest. In order to change your prepared spells, you must take a short rest and use one of your rages, as that is where your most powerful magic is intertwined with your body. 

Spellcasting Ability. Constitution is your spellcasting ability modifier, as the Weave is intertwined with your own body.  

Spell save DC = 8 + your proficiency bonus + your Constitution Modifier

Spell attack modifier = your proficiency bonus + your Constitution Modifier

Spell Limitations. Although you have the Weave woven into your body, your primal instinct still flows and dominates your body. This protect or attack instinct forces you to only be able to cast abjuration and evocation spells through your spell slots.

Magical Awareness

Starting at 6th level, the magic woven into your body has given you the power to identify magic. You can use this feature once. 

You can use this feature twice at 10th level, 3 times at 14th level, and 4 times at 18th level.

You are also now detectable by the Detect Magic Spell

Mystical Rage

Beginning at 10th level, the magical weave has woven into your primal ways. You can now cast spells during your rage (as long as you have a free hand) and you can add your rage damage to your spells when a spell is castes during rage.

Mystical Reaction

At 14th level, your magical power is woven with your entire body, connecting the weave to your primal power. When you get hit with a magical attack, you can use your reaction to absorb the spell's power. You can either take full damage and restore spell slots equal to your barbarian level divided by 3 or take half damage. After using this ability, you must take a long rest before you can use it again.