Base Class: Sorcerer
You innate magic comes from the magic that defines the plane of fire. Perhaps your ancestors bargained with certain powerful fire elementals or maybe have grown up in the fire plane. Any elemental soul might be the originator of these powers for any number of reasons, but they all have one thing in common, a tie to a fire elemental.
Potent Fire
Starting at 14th level, you add your Charisma modifier to the fire damage you deal with any sorcerer spell. You also gain immunity to fire damage.
Fire Familiar
Starting at 1st level, you can cast Find Familiar with the only difference being that whatever creature you choose, is on fire. You can cast any fire spells you have through it, using a sorcery point and the spell slot.
Natural Arsonist
Starting at 1st level you're naturally gifted with fire. Choose one fire cantrip from the sorcerers spell list and you can cast it as a bonus action. And you gain resistance to fire damage
Summon Fire Elemental
Starting at 6th level, your fire elemental familiar can turn into a fire elemental for 3 sorcery points. It must be a fire elemental.
Fire Aura
Starting at 18th level, you can expend 6 sorcery points as a bonus action to gain a Fireball around you, it has a 20 foot radius. While you're in this fireball, any creature that enters your aura other than your allies make a Dexterity saving throw of your spell casting DC for each time they enter it or start their turn in it. If they fail they take 8d6+ your charisma modifer on a failed save or half as much on a successful one.
You remain in this form for 1 minute. It ends early if you are incapacitated, if you die, or if you dismiss it as a bonus action.