The Way of Breathing

Based on a mix of Demon slayer breathing techniques w/ kensei monk 

Total Concentration

as a bonus action you can enter total concentration. When you enter this form and again at the start of your turn choose a breathing technique from those that you know. Requires concentration 1 minute.

Stone breathing

3rd level: When you start total concentration and again at the start of your turn you gain temporary hit points equal to your proficiency bonus.

Water breathing

3rd level: 1d4 ice damage per katana attack.

Damage scaling, 1d6 @ 6th, 1d8 @10th, 1d10 @ 14th

Wind breathing

3rd level: your movement doesn't provoke opportunity attacks. Once per turn you deal additional slashing damage equal to your proficiency bonus when you hit with a katana attack.

Another Breathing style

Gain another breathing style 

Gain a 3rd breathing style

Gain a 3rd breathing style

Additional Proficiencies

When you Choose this subclass you gain proficiency In Longswords.

Water breathing

3rd level: 1d4 ice damage per katana attack.

Damage scaling, 1d6 @ 6th, 1d8 @10th, 1d10 @ 14th

6th level: spend a ki point to reroll concentration save

Stone breathing

3rd level: When you start total concentration and again at the start of your turn you gain temporary hit points equal to your proficiency bonus.

6th level: you can spend a ki point to gain proficiency in any saving throw until the start of your next turn.

Wind breathing

3rd level: your movement doesn't provoke opportunity attacks. Once per turn you deal additional slashing damage equal to your proficiency bonus when you hit with a katana attack.

6th level: you can spend a ki point to extend the range of your attacks by 15 feet until the start of your next turn.

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