Way of the Satsui No Hado

Throughout history, special types of monk have learnt to master their emotion not through intense suppression but by hardening their rage and manipulating it through their ki. These monks can burn through armies and even destroy the soul of their foes. Based on Akuma from SF6.

Level 3: Killer Instinct

You fight with murderous intent. You are always in a state of killer instinct, with flames of rage, passion, and determination envelop you, and you gain the following benefits if you aren't wearing armor:

• When landing a critical hit or killing a creature, you will regain 1 Ki Point. If the killing blow was a technique that used Ki, all Ki spent will be refunded instead.
• At the start of each of your turns in combat, you gain temporary hit points equal to your Wisdom modifier.
• You have Advantage on DEX and WIS Checks and Saving Throws.
• Step of the Wind is changed to Ashura Senku, a Misty Step spell with a range of 15 meters.
• Infuse your Ki into your next strike, enhancing its power and effects.

Empyrean's End

You can spend 1 ki point to launch yourself at an enemy 15 feet near you. The target must make a Constitution saving throw, and take 3d12 fire or necrotic damage. The target takes half as much damage on a successful saving throw. You can increase the damage by 1d12 for every additional ki point spent. At Level 17 and in Demon's Descent, Emperyan's End evolves into Demon's Rage.

Oni's Descent

You can unleash your anger filled energy into your body as a bonus action. For 5 rounds (refreshed as you and your party score kills)  you assume a semi-demon form. In that form your unarmed strikes deal an extra 2d8 fire or necrotic damage, your jump height is multiplied by 5, your speed is doubled, and you gain immunity to fire damage and necrotic damage.

Demon's Rage

Unleash the full power of the Satsui no Hado, and obliterate your foes.  You take a stance, fly towards your enemy (maximum of 30 ft) and hit them with 9d10 fire damage + your Dexterity modifier. On a crit, your enemy is knocked prone. You can add additional 1d10 by using ki point. While in Demonic Descent, you teleport next to a target and grab hold of them, unleashing a deadly dance. All creatures within 15 feet of the target must make a dexterity saving throw to avoid the grapple, if they fail they must then make a constitution saving throw, on a fail they are reduced to 0 hp if their hp is below 150 as the full brunt of the Raging Demon decimates their body and soul, on a success the creatures take 15d10 necrotic damage and are knocked prone.