Monks of the Way of the Martyr learn to absorb some of the damage they take and use this energy when they hit with attack. 

Absorb blows

Starting when you choose this tradition at 3rd level, you can use your ki to absorb some damage when hit by a weapon attack. 

When you would take Bludgeoning, Piecing or Slashing damage you can use your reaction and spend 1 kit to gain resistance to Bludgeoning, Piecing, and Slashing for that attack. After using this feature the next attack you hit with before the end of your next turn will deal extra damage equal to your martial arts die.

Body of Chi

At 6th level you have reinforced your body through meditation. you gain a bonus to max HP equal to 1/2 your wisdom modifier for each level in this class.

*Due to limitations of DnD Beyond you will need to manually add this bonus.

Sacrifice

Beginning at 11th level, you can use your reaction and spend 2 Ki to move up to 1/2 your speed to an ally's space when they are hit by an attack. you push the ally 5 feet in any direction and become the target of the attack which automatically hits you. you gain all the benefits of Absorb blows when you use this reaction. 

Embrace the Pain

At 17th level you can choose to make your martial arts attack with abandon. 

As a Bonus action when you take the attack action you can provoke an attack of opportunity from a creature within 5 feet of you. You can choose to allow this attack to hit you. Any hit is a critical hit.

You can then make 1 Unarmed attack against the creature.

If they took the opportunity attack you gain advantage on the attack

If you are hit you can spend 3 Ki to gain resistance to the damage from the hit and gain a bonus to damage to your attack equal the the damage taken after resistance.

*Example:  You are hit for 50 damage, with the resistance take 25 damage, gain 25 bonus to damage your attack.