Onyx King's Avatar(not tested, pls dont view it)

The tyrant king in a far, far east had a great problem with a peasnt rebelion. The monks from the many monasteries had choosen to help peasnts in their uprisnig and take active part in fighting. Their prowess in combat and connection to Ki turned into an King's obssesion. He commanded all of his schcolars and advisors to allow him and his soldiers to harness the powers of Ki. However druing their reasearch they stumbled into something much more volatile. The power of Ki requires one to devote time and effort to tap into it, to become one with the world, but if you will forcefully harness Ki or catch as it's fleeting back to the world you can mimic the Ki. Thus the King and his Court created the Hei-Ki, and learned to wield it's psychical manifestation the Onyx. The rebelion was a true slaugther, but none of the opposing sides could get an advantage. But one day most of the loyalists  have fallen ill, their bodies just turning to dust. Only some of the lower court members and soldiers that restricted themselves in using those abilities survived and the fleed into the wilderness to creat a hidden villages that later becamed their monastaries. Although not many of those left, The School of Onyx Kings's Avatar are still out there and they try to uphold their traditions and history.

Will of Kings

Starting at level 3, you tap into the power of Ki that is still emiting from the dead, the Hei-Ki. You start to feel the presence of the past souls gathering around your own. As they whisper into your mind you can see a change both in your behaviour and body.
3 of those spirits become close enough to you that you can commune with one of them to gain the following traits:

• The Pale Lady- your skin pigmentation (or fur) turn to the shade of pale gray, as your soul merges with the Lady's, she teaches you how to transfer your own life force into Hei-Ki.
  You can use 10 of your hit points and bonus action to restore 2 Hei-Ki point.
• The Stormbringer- you develop hair and facial hair (includes brows) to a very long length, soul of the Stormbringer shares with knowledge of long forgotten technics to combine weapons of warriors with martial arts.
  Gain proficency with one of the martial melee weapon of your choosing, when using it your Martial Arts ability will work with that weapon however when using two hands to wield a weapon divide your unarmed strike by 2, if the number is fractional round it down (i.e. 1=0; 2=1; 3=1; 4=2 etc.) When you make an critical hit in melee the Stormbringer regains
  1 Hei-Ki points.
• The Azure Sage- your eyes start to glow with blueish gleam when the night begins, when the spirit of Sage allows you to see life force for the taking all around you and shares a secret with you how to aquire it.
  Choose one target (that is not Construct), use 1 Hei-Ki point, roll a spell attack, if succes deal d6 necrotic damage and gain 2 Hei-Ki points. You can use this ability times equal to your monk level per day.

When you commune with those spirits you permamently lose some of you previous monks.

• Ki save DC= 9+ proficiency bonus+Charisma modifier;
• Spell attack bonus=proficiency bonus+Charisma modifier;
• Unarmored Defense- 10+ only your Dex modifier;
• Your Ki energy now becoms the Hei-Ki;
• You regain all your Hei-Ki points after long rest.
• Basic Ki (Flurry of Blows, Stunning Strike etc.) abilites cost is doubled.

Understanding of Hei-Ki

The power of Hei-Ki allows you to bend reality to your will, however the usage of those powers comes at cost. Your body can sometimes not be able to endure the power of those abilites and you can permamently damage your connection to Hei-Ki. Whenever using a Hei-Ki ability make a d20 roll, if you roll a 1, you lose 1 Hei-Ki point forever!

The lost of Hei-Ki point means that your body suffers from sever internal injury and you must withstand the great pain that comes with it. Make an Constitution Save, on failure
lose 10 HP.

Here is list of Hei-Ki abilities: Cost, Casting Time, Duration,

• Mark- touch a target, leave a small crystal dart in its body, lower target's AC by 1, and the target becomes marked.
  1 Hei-Ki, bonus action, 1 round.
  
  
• Black Fists- infuse your hands with the power of Hei-Ki, the skin on the outerlayer of  your hands transform into black crystals: Unarmed Strikes: +1dmg. If you hit marked target the effect is prolonged until your next turn.
  1 Hei-Ki, bonus action, 1 round.
  
  
• Crimson Onyx- you can creat a cluster of red onyx crystals, they posses the properties of fire, you can apply them to one chosen weapon (yours or allies). On hit add 2d4 fire damage. The crystal can be crushed or thrown to start a fire. If you use the Black Fists you can apply Crimson Onyx to your unarmed strikes. You can throw the cluster at target that is marked in order to deal 2d4 fire damge, but target can make dexterity save.
  2 Hei-Ki, bonus action, 4 rounds.
  

• Killing Intent- you spread the onyx miasma that manifest the power of mind to up to 3 targets within 20ft, enemy must make an Wisdom save, if failed deal 2d4 psychic damage to the target and it's next attack have disadvantage. If succeded deal d4 psychic damage. If target is marked it becomes frightend.
  3 Hei-Ki, bonus action, 2 rounds.
  
  
• Onyx Orbs- summon 4 crystal orbs, each orb grants you 3lvl-1AC/8lvl-2AC/13lvl-3AC. The orb is destroyed after an attack on you. If target is Marked you can command all of your orbs to attack target for d4 buldegonig damage each. After an attack orb is destroyed.
  4 Hei-Ki, bonus action, 4 rounds.
  
  
• Dancing Shards- break a metal weapon that you are currently holding in your hands, the shards of it become 4 blades covered with black crystals. You can command the blade to attack which will require target to make an Dextirity save, if it failed you damage the target for d6 piercing damage, if all 4 of the blades hit make a damage roll as if the broken weapon hit the target. The weapon shards are destroyed whether the blades hit or miss. If target is marked your Blades hit always.
  4 Hei-Ki, Metal Weapon, bonus action.
  
  
• Shiftwave- stomp your leg into the ground and cause its surface to change into black, polished tile within 40ft radius, if there is obstacle in the way or wall the tile is created on it. You are able to sink into tile and emerge anywhere on it as bonus action. If target is marked and is on the tile surface you can touch them to submerge it into the tile and restrain it.
   Target must make an Strength Saving throw to free itself.
  5 Hei-Ki, 1 turn, 4 rounds.
  
  

False Death

You can creat an effect on a creature that is willing to partake it and is concious. The effect makes the target to appear dead. The magical and pshysical examination will not help to detect it, unless the target is taking damage. You can upheld this effect on target for minutes equal to your monk level. However if you use this on yourself you cannot stop this ability. Target can make an inteligence save to try to remember what happend with and around their body during the ability.

Spiritual Attunement

You can once again commune with spirits of the dead that surround you. Choose to creat a bond with one of the spirits from the Will of Kings or to improve the connection with one of them, should you choose to do that you will:

• The Pale Lady --> The Pale Queen- your skin (or fur) turns from the light grey to true white. Likewise your eyecolour becomes a lighter shade of the one you have right now.
  You master an ability to transfer your own lifefore into Hei-Ki. 5HP points can be exchanged into the 2 Hei-Ki points.
• The Stormbringer--> The Tempest- your long hair now turn to a shade of blueish dark,when using a martial weapon you deal d4 additional lightning damage and if you roll on melee attack 18,19, 20 you regain 1 Hei-Ki point.
• The Azure Sage--> The Azure Scrollmaster- your eyes now glow constantly with a blue gleam, when you succsefully steal the life force gain 3 Hei-Ki points.

The True Asciension

For a moment you grasp a soul of the Onyx King, he grants you his powers on a condition of using 10 Hei-Ki points, you can use this ability once before long rest. You creat two additional arms made entierly of black crystals. Around your head floats a black, 4-pointed, crystal crown. All your hands have the effect of Black Fists. You can wield additional weapon. You can make an additional attack with your new pair of hands. The effect lasts 5 rounds. During this time you can use one of those special abilities:

• Turn to ash before us! - the crown flies in front,as you grab it, you transfer your energy through your arms and fire a blast of red onyx's power. You make an spell attack, the foes in front of you, to 20ft, the beam is 5ft wide, are smited for 5d8 fire damage. It takes 1 action to cast.
  
  
• Kneel! - you strike the ground with all of your 4 arms, the might of the strike turns ground in front of you to difficult terrain in 30ft. Additionally all foes in the zone must make constituion save, when they fail they're knocked prone and take 2d6 bludgeoning damage and 2d4 thunder damage. It takes 1 action.
  
  
• We see you!- you clench your fists, you send a sprout of small crystals from your body in 30ft radius, all targets within become marked, when a target that is marked is killed you gain 4 Hei-Ki points and 2 Health Points.