The Fighter becomes a one-armed samurai, but walks with the power of a yokai within them. Their missing arm becomes an oni's arm, and through it they gain a new arsenal of techniques to deal heavy damage and increase their endurance.

Oni State

At the 3rd level, the Fighter has access to Yokai Techniques, in exchange for their left arm. They are unable to equip shields, offhand weapons, or use a versatile weapon with two hands. Upon using a Yokai Technique, the fighter must make a CON saving throw of 12 or take exhaustion.

When the Fighter uses a Yokai Technique, they enter the Oni State until the end of their next turn. During this state, the Fighter gains +1 to AC and +1 to attack rolls.

Oni State grants +2 to AC and Attack rolls at the 11th level, and +3 to AC and Attack rolls at the 18th level.

Yokai Technique: Cyclone

As an action, the Fighter summons their Yokai arm, spinning with a fierce backfist. All creatures within a 5 ft radius of the Fighter must roll a DEX Saving Throw. Upon a failed save, creatures take 2d6 Bludgeoning Damage and are knocked prone and pushed back 5 feet from the Fighter. Upon a passed save, take half damage without being moved.

Yokai Technique: Slam

At the 7th level, the fighter can use their yokai arm for a quick strike. On a bonus action, deal 2d6 bludgeoning damage to an enemy within 5ft. Upon successful hit, the enemy must pass a CON Saving Throw or be stunned until the end of the Fighter’s next turn. Targets within 5 ft of the impact radius must pass a DEX Saving Throw or be knocked prone.

Yokai Augmentation: Kanabo

At the 10 level, the fighter can now use the Kanabo when using Yokai Techniques.

The range of all yokai techniques increases by 5ft.

After using Kanabo Techniques, the Fighter gains access to 1 total use of Kanabo as an attack while in the Oni State. The Kanabo attack deals 2d6 bludgeoning damage.

The Fighter has 2 uses of the Kanabo Attack at the 15 level, and the damage raises to 2d8.

Yokai Augmentation: Momentum

At the 15 level, if the Fighter successfully lands a critical hit, their next Yokai Technique can be done without risk of exhaustion.

If a roll for Slam or an attack using Kanabo is lower than 10, the roll will become a 10 automatically.

Yokai Augmentation: Indomitable

At the 18 level, when the Fighter receives damage while in the Oni State, they may reduce oncoming damage based on their CON Modifier. This benefit no longer applies when the Fighter has exhaustion effective, or if the damage is dealt by a purified weapon or magic. (Note: check with your DM on what counts against Yokai).

The Fighter also gains advantage on rolls for the recoil of Yokai Techniques.