Fire Soul Knight

The archetypal Fire Soul Knight harnesses the destructive and restorative power wielded by druids of the circle of wildfire. Connected to the natural power of fire, they draw from their awakened spirit, a fiery soul hidden deep within each person. Using this power they control flames both to lash out at those they face in combat, and to heal wounds caused by an enemy’s blade. 

Burning Strike

Starting at 3rd level, you can infuse your weapon with the fire of your spirit. As an action, you can make a melee weapon attack against a target. On a hit, the target takes the weapon's regular damage and an additional 1d8 fire damage. This damage increases by 1d8 at 7th level (2d8), 10th level (3d8), and 15th level (4d8).

You can use this feature a number of times equal to your constitution modifier (a minimum of once). You regain all expended uses when you finish a long rest.

Kindle the Soul

Also at 3rd level, you learn to transfer your spirit to another person, healing wounds and injuries. As an action, you can touch a creature and sacrifice a number of hit points. That creature regains hit points equal to the number hit points sacrificed, not exceeding their maximum hit points.. This feature has no effect on undead or constructs.

Once you use this feature, you must finish a short or long rest before you can use it again. 

Spirit Lock

Starting at 7th level, you learn to link your opponent's spirit to your own. As a bonus action, you may attempt to link a creature's spirit within 60ft of you. The target must make a Constitution saving throw with a DC equal to 8+your Constitution modifier+your Proficiency Bonus or become spirit-linked. While spirit-linked, the affected creature cannot willingly move further away from you, and has disadvantage on attack rolls against creatures other than you. Additionally while spirit-linked, the affected creature becomes one stage more vulnerable to fire damage (immunity becomes resistance, resistance becomes regular, regular become vulnerability). The creature can reroll the saving throw at the end of each of its turns, ending the effect on a success.

Once you use this feature, you cannot do so again until finishing a long rest.

Cloak of Flame

At 10th level, you learn how to use a slain enemy's spirit to protect you in combat. When a creature that has been hit by your burning strike in the last minute dies within 60ft of you, you can surround your body in a shield of flame made from the creature's spirit, granting you a bonus to your AC equal to your Constitution modifier for the next minute. You can only benefit from one instance of this bonus at a time.

The slain creature cannot be an undead or construct to use this feature. 

Soul Wings

At 15th level, you gain the ability to manifest your spirit as a pair of fiery wings resembling those of a phoenix. You can summon the wings as a bonus action on your turn, and they last until you dismiss them as a bonus action. While the wings are summoned, you gain the following benefits:

• You gain a flying speed equal to your current speed
• You gain resistance to fire damage
• You shed bright light in a 20ft radius and dim light for additional 20ft
• A creature that hits you with a melee attack takes 2d8 fire damage

Any flammable clothing you are wearing when you summon the wings may be set ablaze when you summon them. 

Empowered Spirit

Beginning at 18th level, you learn to manipulate the spirit of others through your flames. Whenever you deal fire damage to a creature, you heal a number of hit points equal to half the fire damage dealt rounded up.