Graphite is the pure carbon stuff of pencil leads. It is used in high temperature crucibles.
GRAPHITE CRUCIBLES - TEMPERATURE RANGE
The crucible material must have a much higher melting point than that
of the material used in it for processing. Graphite crucible can
withstand high temperatures, are chemical and thermal shock resistant.
Graphite crucible is ideal for the melting of Aluminium, Copper, etc.
Graphite Crucible Temperature Range can go as high as 5000°F and can
be used in furnaces and high heat processes.
It is rated stable up to 6700F - provided there is not oxygen to oxidize it. At higher temperatures, absent oxygen, it degrades by sublimation which I found in the abstract of this article looking at graphite for atmospheric re-entry shields. Pure carbon vapor is a weird thing to think about. Probably it turns back into soot pretty fast. Stuff will get dirty during this fight.
Even if there is oxygen, at those very high temperatures the density of oxygen ready to react will be very low, and the escaping CO2 from oxidizing graphite will tend to make a cloud of CO2 over the graphite, which will protect it from incoming oxygen. You will in essence have an ablating heat shield, which can disperse heat by gradually reacting away.
A nice thing for your story is graphite is familiar. If I read about an exotic supermaterial like silicon carbide in the context of a fiction I would assume it was made up by the author. Readers will be familiar with graphite as a substance. Your heat shield will be a badass matte black,. Also the ablating heat shield will make all kinds of smoke and gas which will be impressive.
And you could use your heat shield to sketch insulting pictures of your enemy. Your sidekick can carry an eraser.