This class of Sorcerer gains their innate abilities from their connection to the Plane of Fire.  This connection could be through blood, such as a genasi, or perhaps exposure to elemental forces during childhood.  Sorcerers with this connection use their command of fire to create white hot infernos, purging their enemies from the earth.  More powerful elemental sorcerers walk into volcanos in nothing but a flimsy robe, and walk back out unscathed.

Fiery Blood

At 1st level, you gain resistance to fire damage.  In addition, you can cast burning hands at 1st level once without expending a spell slot.  Once you do so, you cannot again for until you take a short or long rest.  Instead of Charisma, you use Intelligence as your spellcasting ability for all spells.

Inner Blaze

At 1st level, when you cast a spell that deals fire damage, you can add your Intelligence modifier to the damage.

Mark of the Flame

At 6th level, you can spend 3 sorcery points as a reaction if you take fire damage.  You gain immunity to all fire damage for 1 round, including the triggering damage.

Molten Touch

At 14th level, your unarmed strikes deal 1d8 fire damage.  In addition, you can cast the spell inflict wounds at 4th level once without expending a spell slot.  Instead of necrotic damage, this spell deals fire damage.  You must complete a short or long rest before using this ability again.

Child of the Inferno

Beginning at 18th level, you can channel the fiery power of your elemental connection, causing your skin to catch fire. As an action, you can spend 5 sorcery points to draw on this power.  It lasts for 1 minute.  While activated, you have immunity to fire damage, a flying speed of 30 ft., and the ability to cast fireball at will.   In addition, whenever a creature within 10 ft. of you hits you with an attack, they take 2d6 fire damage while this ability is in effect.  You shed bright light in a 20-foot radius, and dim light for another 20 feet.  While in this form, you can spend 10 sorcery points as an action and cast meteor swarm without expending a spell slot.  Once you do this, you can't do it again for one week.