Demon Slayer.

Demon slayers are high endurance combatants that carefully regulate their breath usage in battle; making use of a special breathing technique that laces their strikes with elemental energy. Originally created to fight against demons more modern demons slayers have adapted their techniques to deal with a wide variety of foes. 

Deep breath

When you choose this archetype at 3rd level, you possess 4 breath points and gain an additional point at 7th and 15th level. These points can be used to activate your Opening Thread feature. Breath is regained after a short or long rest.

Opening Thread

Starting at 3rd level, you can manipulate your breathing to create threads of invisible energy. Choose a damage type between acid, cold, fire, lightning, poison, or thunder.

As a bonus action, you can spend 1 breath point to enter total concentration for 1 minute; while in total concentration, you can mark a creature you can see with your opening thread. While marked, you deal an additional 1d4 ((breath damage type)) to the creature whenever you hit them with a melee attack. You can only have one creature marked at a time. Marking another creature ends the previous mark.

This damage increases to 2d4 at 7th level and 3d4 at 15th level.

Quick Sense

Starting at 7th level, you’ve learned to perceive your surroundings at an alarmingly fast rate. You gain proficiency in the Perception skill. If you already have proficiency, your proficiency bonus is doubled for checks you make with it. You also can’t be surprised if you aren’t incapacitated.

Evade and Counter

At 7th level, when a creature within your reach misses you with a melee attack, you can use your reaction to spend a breath point to make a single weapon attack. 

Recovery Breathing

Starting at 10th level, when you use your Second Wind while you have no Breath Points remaining, you regain all expended Breath Points. Once combat ends, you gain one level of exhaustion.

Total Concentration Constant

Starting at 15th level, your breathing has become instinctive, allowing you to maintain perfect focus even in the heat of battle.

While you are in Total Concentration:

• Your speed can't be reduced, and difficult terrain doesn't cost you extra movement.
• You have advantage on Constitution saving throws.
• When your marked creature is reduced to 0 hit points, you can immediately mark another creature you can see within 60 feet without using a bonus action.

Demon Mark

Beginning at 18th level, you can awaken the power hidden within your body. As a bonus action, you expend 3 Breath Points to activate your Demon Mark for 1 minute.

While your Demon Mark is active:

• You have advantage on attack rolls against your marked creature.
• Once on each of your turns, when you deal Opening Thread damage to your marked creature, each other creature of your choice within 10 feet takes Opening Thread damage equal to your current Opening Thread damage.

You can only use this feature once per long rest.