Ronin

"A flash of steel, like a conductor’s baton guiding a symphony of slaughter, heralds a helix of death and honor. A blur whips from tree to rock to shadow; corpses fall in its wake."

The Ronin are masterless, wandering warriors, beholden to no code but their own. No two are the same, each with their own tale that led them down the warrior’s path. They are masters of many weapons, striking with blade and arrow in a spectacle of blinding speed and accuracy. Some ronin use their power to protect the vulnerable as vigilantes doing what they see as right, no matter the cost. Others pursue their own ends, unfettered by the consequences of their actions. Ronin are dangerous combatants, hardened survivors, and above all things, free. Occasionally a Ronin teams up with other Ronin for a greater cause. Ronin follow a very strict code in their lifestyle and they are never scared of death.

I am my Master

When you choose this archetype at 3rd level, you gain proficiency in an additional skill of your choice, learn a new language of your choice and also gain proficiency in a tool of your choice.

Spirit of Ronin

Starting at 3rd level, your intensity in battle can help you strike true with rapid speed. As a bonus action on your turn, you can give yourself advantage on weapon attack rolls until the end of the current turn. When you do so, you also gain temporary hit points equal to double your proficiency bonus.  When you take attack action after using spirit of Ronin, the first attack that hits deals 1d6 + half your fighter level extra damage of the weapon's damage type. 

You can use this feature upto number of times equal to your proficiency bonus, and you regain all expended uses of it when you finish a short rest.

Slash parry. While you have the temporary hit points from the spirit of Ronin, you can take a special reaction called slash parry. When you are hit with a melee attack while you have the temporary hit points from your spirit of Ronin, you can use your reaction to make a melee weapon attack with advantage against the creature that attacked you. You don't need to have a melee weapon drawn  in your hand to make this attack, but the weapon must be on you.

Iron will and Motor Learning

Starting at 7th level, your discipline and attention to detail allow you to excel in both combat and social situations. You will develop Iron will and Motor learning.

Iron will. You gain proficiency in WIS saving throws.

Motor Learning. When you make an ability check, you can use your reaction to add your constitution modifier to the roll. You can use this feature a number of times equal to your proficiency bonus. You regain all expended uses when you finish a long rest.

Relentless Onslaught

The speed and ferocity of your onslaught is legendary. Starting at 10th level, when you take attack action, each time you score a critical hit you can make one additional weapon attack as a part of the same action and you also regain one expended use of Spirit of Ronin. Additionally, if you kill a significant hostile creature (at DM's discretion) on the battlefield, you regain one expended use of spirit of Ronin.

Third Wind

Your urge to fight and protect your allies and the wronged is strong. Starting at 15th level, your fighting spirit keeps you fighting against all odds. When a damage reduces you to 0 hit points and you are not dead, you can make a constitution saving throw (DC 5 + the damage taken to bring you to 0 hp). On a success, you instead drop to 1 hit point. You can’t use this feature if you are reduced to 0 hit points by a critical hit.

After the saving throw succeeds, you can’t use this feature again until you finish a long rest.

Honor in Death

As a Master Ronin, you don't fear death but crave honor in it with one last burst of ferocity. Starting at 18th level, your Spirt of Ronin can delay the grasp of death. If you take damage that reduces you to 0 hit points and doesn’t kill you outright, you can use your reaction to delay falling unconscious, and you can immediately take an extra turn, interrupting the current turn. You also immediately gain the benefits of Spirit of Ronin this turn even though you have no uses of it left. While you have 0 hit points during that extra turn, taking damage causes death saving throw failures as normal, and three death saving throw failures can still kill you. After this extra turn, you will either fall unconscious or dead only if you lose your temporary hit points from Spirit of Ronin and still have 0 hit points.

Once you use this feature, you can’t use it again until you finish a long rest.