Impenetrable
At level 1, you gain the Armament Attunement and increase your maximum hit points by 2 and for every additional level in this class that you gain increase your hit point maximum by another 2.
Hunker Down
When you reach level 3, your AC when unarmored is equal to 10 + Proficiency + CON Mod. If you have not moved yet you can use your Movement Action to reduce your movement speed to 0 for your turn. If you choose to do so you gain a +2 to AC and DR equal to your Proficiency Bonus.
A Strong Defense
At level 6, you gain access to a resource called a Hardening Pool. When entering and exiting initiative your Hardening Pool is set to 0. Whenever you are hit by an attack roll or fail a saving throw, you gain points in your Hardening Pool equal to half the damage you take, or would have taken. You can only have a maximum number of Hardening points in your pool equal to 5 x Your Haki Master level. As a Bonus Action you can spend points in your Hardening Pool for the following effects.
5 Points: You gain 2 DR for the Round (to a maximum of 6 DR per round).
8 Points: You gain 1 AC for the Round (to a maximum of 3 AC per round).
12 Points: You gain 1 DR for the Combat. (To a maximum of 15).
20 Points: You gain 1 AC for the Combat (To a maximum of 3).
Additionally, you can spend 15 points from your Hardening Pool as a reaction to turn a critical hit against you into a normal hit.
Rock Hard Recoil
Starting at level 10, you gain resistance to either bludgeoning, piercing, or slashing damage; you can change your selection on a Long Rest. A number of times equal to half of your Proficiency Bonus rounded up, when you are hit by a melee attack or technique you can deal damage equal to your DR to the attacker per Long Rest.
Adamantine Defense
At level 13, your mastery of Armament Haki allows you to further solidify your defense. You gain the ability to use your Hardening Pool to prevent harmful conditions. When you would be subjected to a condition (such as paralyzed, stunned, or poisoned), you can spend 15 points from your Hardening Pool as a reaction to negate the condition. Additionally, you can extend your defensive capabilities to allies. Once per long rest, you can spend 25 points from your Hardening Pool to grant an ally within 30 feet 10 DR for 1 minute.
Flame Pattern Coating
You've developed your hardening Haki to the peaks of defense. At level 17, once per short rest you may use your Hardening Pool and a Bonus Action to perform one of the following Effects.
50 Points: You gain 30 DR for 1d4 Rounds.
60 Points: You gain 4 AC for 1d6 Rounds.
70 Points: You gain resistance to a Damage Type of your choice for the rest of combat.
Ultimate Defense
At level 20, your defense reaches its pinnacle, making you nearly invincible. You gain a permanent increase of 10 points to your Hardening Pool maximum. Additionally, once per long rest, you can activate your Ultimate Defense as a reaction, spending 80 points from your Hardening Pool. For the next minute, you gain immunity to one damage type of your choice and a +5 bonus to your AC.