They don't know him.
They think they do: Grantaire the cynic, Grantaire the drunkard, Grantaire the useless - but they don't. He's made sure they don't, because if they did, if they knew who he was, it would be him chained up in there instead of the Inspector.
(It must say something about him - or how very far he's fallen - that the Inspector didn't know him even when he'd stared Grantaire right in the face.)
He fights through the first attack with the others as their equal and nothing more: that's what Enjolras wants of him. That's what he's trying so very hard to believe in, even though he knows they are doomed, knows that this rebellion was dead before it began. They're only facing soldiers for now and so they're holding out behind the barricade and giving each other congratulatory smiles and shouts, but it won't last.
Grantaire can already smell the smoke in the wind. He can tell the others can't yet: they're too cheerful, too alive, they don't realize. Paris is burning; the 'benders are out, marching from pile of wood to pile of wood and drowning the fires of rebellion in the King's Fire.
He takes another long draw of brandy as the others continue the song he began. He'll die here with them, with his friends, he thinks. That's all right. He can't think of anywhere he'd rather die; there's a certain romance in the idea of burning with Enjolras, of letting the flames consume them both: one blade for Pyramus and Thisbe, one pyre for Enjolras and Grantaire.
Romance, he thinks, and laughs at himself. He's as bad as Marius. I feel my soul on fire.
Someone - he's not sure who, the world is muffled and smoky already and growing darker every moment - elbows him in the gut and reports to the barricade at large: "Grantaire is drunk."
This isn't news to anyone.
Grantaire wakes to a voice from the past, calling to them from beyond the barricade to lay down their weapons and not throw their lives away. He pries his bleary eyes open in time to see Enjolras scrambling down, his face grim, a tiny flicker of fear alight in his eyes for the first time since Grantaire saw him preaching revolution and promptly threw his life under Sisyphus's boulder.
"We're the only ones left," Enjolras says. His voice is as steady as ever; he stands straight, broad-shouldered, and perhaps Grantaire is the only one who sees anything else. "The firebenders have come." (It is only at this point that Grantaire realizes the smoke in the air is now thick enough that the others smell it too.)
A silence descends, a snuffed candle still smoldering, and then Enjolras is telling the others to leave if they wish but the fight will go on - and Grantaire, unnoticed, starts hauling himself up the shattered chairs and broken tables until he can see over the top of the barricade. The street is full of men, a regiment of soldiers in front, living shields, and behind them the firebenders. There's no way out of this that doesn't end in death.
He doesn't remember who it was that snarled at the Inspector that there were some things that never died, but he's pretty sure they had been talking about idealism or Enjolras's Patria. Right now, though, Grantaire decides that what he wants is for Enjolras to not die, not today.
There's one mouthful of brandy left in his bottle and Grantaire gulps it down, savoring the harshness across his tongue, the fumes curling in his throat, then hurls the emptied bottle over the barricade. It shatters in the midst of the common soldiers with a satisfying crash.
Shouts from in front of him, mostly of alarm, and from behind him - "Grantaire!" but Grantaire is not listening. Before they can start shooting again, he snaps his fingers to call the flame and breathes with everything he has in him, a great dragon's roar that fills the street from side to side.
They were not prepared - of course they weren't, how could a firebender stand with the rebellion? - and it takes them full force, burning soldier and 'bender alike with consuming fury, white gouts of fire licking up the buildings and heating the cobbled street to glowing and still Grantaire breathes until there is nothing left but black fluttering ash and the world is growing dim again and they are safe for the moment.
Someone - Combeferre? - grabs him about the waist and hauls him back from the edge of the barricade. Strengthless, he collapses where he's dropped, on a battered, slashed mattress. He thinks they are saying something, but all he hears is the crackling rage of fire and the sound of his father's voice.
And then Enjolras is leaning over him: his eyes are wide but the fear from before is quenched. His lips move unintelligibly; Grantaire-who-is-not-Grantaire smiles muzzily up at him and faints.