Darkin Bound

Bound by shadow and deep magic, the Darkins are an ancient race that has been corrupted by the void wars. Ascended from Shurima falling to corrupt ways and therefor their fate being chained to corruption, death and decimation. In order to stop their spread, they were imbued into weapons that would hold them captive to some extent. That is, until some unfortunate soul finds that powerful weapon and begins to wear on that person's mind. Now the person is chained to the weapon, forced to be in a constant mental battle for control and to not fall into the power that the Darkin offers.

 

Bound by shadow and deep magic, the Darkins are an ancient race that has been corrupted by the void wars. Ascended from Shurima falling to corrupt ways and therefor their fate being chained to corruption, death and decimation. In order to stop their spread, they were imbued into weapons that would hold them captive to some extent. That is, until some unfortunate soul finds that powerful weapon and begins to wear on that person's mind. Now the person is chained to the weapon, forced to be in a constant mental battle for control and to not fall into the power that the Darkin offers.

The Corruptive Lure 

Darkin weapons radiate with magical and infernal energy, so many magically adept races are able to detect these negative energies. So due to location and their occasional obliviousness, humans are the most likely victim to these alluring weapons. There is a decent chance that the person is able to live in somewhat of a symbiotic relationship with the Darkin, them being able to use the magical benefits of the weapon to their advantage and resisting the constant pull of power that the Darkin emits. More likely than not though, many fall to this power and become vessels for the Darkin. Evolving into a demon like entity that holds great strength and hidden abilities.

Aspects of the Darkin

Each of the Darkin descend from the Gods of Shurima and therefor have a certain aspect that relates to their previous godhood. It is said that if a Darkin were to die the related aspect would leave from this world and change into something else entirely. The death of a Darkin, and their respective aspect, will die if they are left without a host and the efforts of those who worship the Darkin. The Darkin looks to control the host to draw their strength and energy to ultimately control their body. However, the Darkin is at the mercy of a person with a powerful mind, because simply discarding the weapon relieves them of their corruption.

Names

Names follow typical human names for the wielder of the weapon however, the Darkins have very different names that typically relate back to their Shuriman heritage. (These are just examples you can use these or take them as inspiration.)

Male Darkin Names: Aatrox, Varus, Rhaast, Akmenos, Amnon, Barakas, Damakos, Ekemon, Iados, Kairon, Leucis, Melech, Mordai, Morthos, Pelaios, Skamos, Therai

Female Darkin Names: Akta, Anakis, Bryseis, Criella, Damaia, Ea, Kallista, Lerissa, Makaria, Nemeia, Orianna, Phelaia, Rieta

The Corrupt Bond

At 3rd level, you become bonded to a Darkin Weapon(At your DM's discretion) and are unable to equip or use any other weapon while using this class. This weapon is considered magical and for as long as you are bonded to it, it cannot be stolen, lost, traded or sold. 

The Darkin Weapon grows in strength the most carnage it commits growing in strength and ability. See the growth rate below:

5 Final Blows: +5ft Attack Range (Max +10ft Bonus)

10 Final Blows: +1 to Hit

15 Final Blows: +1 to Damage Modifier

20 Final Blows: +1 Appropriate Damage Die (Depends on what kind of weapon)

This list can scale infinitely, but can be changed or have a limit based on your DM's discretion. Killing CR 15 or higher will automatically advance you five kills in the progression. The weapon is able to be renounced and you can then equip other weapons, but in doing so you lose all point progress and all benefits of the weapon. Points cannot be earned again until the weapon is re-equipped. 

Corruption Consumes

While using the Darkin Weapon the user is able to succumb to the wishes of the Darkin and transform into a hybrid that primarily has Darkin abilities. While in this form you gain temporary hit points equal to your Final Blow count (Before 5 final blows are achieved you have a minimum of 5 Temporary Hit Points).

Your Darkin form also is able to have a choice of wings, webbed appendages and gills or sharp claws each giving a different benefit. Only one attribute may be picked,

Wings: Flying Speed 25ft

Webbed Appendages and Gills: Can Breathe Underwater and Swim Speed 35ft

Sharp Claws: Dig Speed 10ft per Second, +2 to Unarmed Strike

Whilest in this form it deals a damaging toll on the host's body and the mind begins to weaken. At the start of each turn in combat(or every 10 minutes out of combat) The host takes 1d4 psychic damage(1d6 at lvl 7, 1d8 at lvl 15, 1d10 at lvl 18) that goes through any temporary hit points. This damage will persist till the Darkin Form has ended. 

The transformation ends when the host rolls a successful Constitution saving throw (DC 15) to release themselves from the Darkin or the host falls unconscious  

Siphon Carnage

Beginning at 7th level, when dealing damage with your Darkin Weapon within your Darkin Form you heal for half of the damage dealt.

Spite Channeled

At 10th level, you learn how to turn your pain into your enemies own downfall. When you take amounts of damage you charge Spite. Activating the channeled spite does damage around you in an area of effect. See list below for charge thresholds:

20 Damage Taken: 1d12 in a 5ft radius

30 Damage Taken: 2d12 in a 10ft Radius

40 Damage Taken: 3d12 in 15ft Radius

50 Damage Taken: 4d12 in 20ft Radius

Once a threshold is achieved it can be activated for the appropriate effect or can be saved for a later effect. This stacks until hitting a total of 50 damage in which it cannot exceed that total. Taking more damage over the 50 does not contribute to the next instance of stacking. Once a short or long rest has been accomplished all stacks of damage taken disappear. 

Killing Bloodlust

At 15th level, When you use your action surge you are able to move an additional 20ft on your turn and you regain your Final Blow Temporary Hit Points. (Temp Hit Points do not stack)

Darkin Adeptus

Starting at 18th level, You and your Darkin have achieved an ultimate symbiotic relationship and are able to greatly benefit one another. Your Darkin weapon heals you for half damage done by the weapon even when not in Darkin Form. Your Darkin form is also greatly enhanced and whilst in it you get increased abilities. You now heal for all damage dealt, gain 30ft of extra movement and once you have dealt the final blow on a target you regain one attack and all movement.