Gunbreaker

Many hundreds of years ago, in a land seemingly lost to the expanse of time, a queen resided over the land.  Keeping her safe, was her royal vanguard, the Blades of Gunnhildr.  Their training was extensive and diligent, surpassing much of the acumen of other military forces - their secret lay within their unique technology, the gunblade, a weapon capable of infusing the users own power into devastating blows or defensive techniques utilizing the cartridge system built into the weapon.

 

Many generations passed, and the true purpose of the Blades began to fade into obscurity, and their means of being passed along rapidly dwindled as practitioners of the craft began to decline - those that are left act as mercenaries, offering their protection to those willing to pay the price of a lost art being under their employ, but seldom is a gunbreakers employer disappointed.

Gunblade Proficiency

When you choose this martial archetype at 3rd level, you gain proficiency with gunblades, the signature weapon of the gunbreaker.  Gunblades utilize the long sword stat block, and proficiency allows you to add your proficiency bonus to your attack rolls.  Certain abilities will force your target to make a save against your gunblade DC, which is calculated as 8 + proficiency bonus + your Strength modifier.

Aether Cartridges

Starting at 3rd level, you unlock the core feature of your gunblade and are able to utilize cartridges to fuel certain abilities used by this class.  You start with three, and regain all charges on a short rest.  You gain additional charges at 7th, 10th, and 15th levels.

Vanguard Oath

At 3rd level, your training has given you more ways than one to defend against attackers.  Choose one of the following: 

Brutal Shell

The best offense is a good defense - when you successfully land an attack against a target, you can choose to expend a cartridge to heal yourself for the damage you dealt with your gunblade.  Additionally, gain temporary hit points equal to the amount healed.  If your hit points are already at maximum, you won't benefit from the healing effect, but you'll still gain temporary hit points.  This effect can only be triggered once per round.

Parry

Starting at 3rd level when you select this feature, you can use your bonus action to add +2 to your AC as long as you have at least one cartridge, which lasts until an attack successfully hits you, you lower your guard to cancel the action (no action required), or you use the next feature.  If you're subjected to an attack that misses, you can use your reaction to expend a cartridge and deal 1d10 thunder damage to the attacker.  The attacker must roll a strength save against your gunblade DC, or be pushed back 5 ft.  You don't lose a cartridge unless you use your reaction, even if your guard is broken or you cancel the action.  Once you use this reaction, parry ends.  The damage from this feature increases to 2d10 at 10th level.

Lightning Shot

At 7th level, you've tuned your blade to deliver blows from further away.  When you take the attack action on your turn, you can do so with a ranged attack of 20 feet instead, dealing 1d6 plus your STR modifier.  You are proficient with the attack.  You can only use this ability once per turn.  Additionally, intense usage of your cartridges has coated your gunblade with the remains of your shells - your weapon attacks are now considered magical for the purpose of overcoming resistance to nonmagical attacks and damage.

Royal Guard's Vow

Starting at 10th level, your vow to defend grants you further resolve, choose from one of the options below:

Aurora

In your line of work, a helping hand can be the difference between life and death - as a reaction when you or another creature within 20 feet of you takes damage, you can spend a cartridge to offer a moment of reprieve in the form of 2d6 + proficiency healing.

Nebula

With hardened resolve comes a hardened exterior to match - as a bonus action, you can use fire a blank round that coats your body in a damage-reducing barrier.  For the next minute, you have resistance to piercing, bludgeoning, and slashing damage.  You can use this feature a number of times equal to half of your proficiency bonus rounded down, and all uses are recharged on a long rest.

Heart of Stone

With determination and grit, you're prepared for the worst.  Starting at level 15, you can cast Heart of Stone on an ally as an action.  The chosen target gains a +2 to their AC for the next minute.  Additionally, the targeted ally now has a 30 ft aura around them that grants +1 AC bonus to any allies within the aura.

Iron Will

Your expertise in your craft has reached its peak, and you will never back down from your foe.  At 18th level, choose one of the following features:

Heart of Corundum

Your stalwart soul shines through, this upgrades Heart of Stone.  When you use this ability, you cry out to nearby enemies to draw their attention to you, giving disadvantage on attack rolls to any allies in the aura other than yourself.  The effect ends if you leave the aura.

Heart of Light

You are a beacon of hope to those that you choose to protect - as an action on your turn, you project a 30 ft radius around yourself, granting nearby allies temp hp equal to your fighter level at the start of each of your turns.