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Tanjiro isn't breathing.
He isn't breathing and the Kakushi with his finger pressed to Tanjiro's throat says there's no pulse, but it can't be true, it can't be.
Giyuu is moving before he realizes it, forcing himself upright. His whole body fights him. It's like wading through a waist-deep current, limbs slowly turning to clay, and vaguely he registers the Kakushi trying to keep him down.
Giyuu rolls his shoulder and then no one is touching him and, somehow, his legs are carrying him forward.
Tanjiro is kneeling, uniform spattered in blood, his head bowed and hiding the damage Kibutsuji did to him. Still and cold.
The memory of Tanjiro's smile flashes into Giyuu's mind and—
"Do you have any siblings, Giyuu-san?" Tanjiro seems to realize the potential delicacy of the question as he asks it. A look passes over his face, like he just accidentally stepped on something and heard it snap in half.
Giyuu turns away, hiding whatever expression he might be making. The countryside around them is gently rolling hills and scattered white birch, everything a bright happy green in the midday light. A breeze flutters the sleeves of his haori about his wrists.
"… I had an older sister," he says. He makes sure that his voice betrays nothing, calm and flat. Then he looks at the road ahead again, throwing a sidelong glance towards Tanjiro for his reaction.
At his side, the young boy beams. "So you're a little brother! That's funny."
Giyuu raises one eyebrow. What about that is funny, he wonders.
"Just 'cause…" Tanjiro answers his unasked question, scratching idly at the back of his head. "You act like such a big brother to me."
Once again, Tanjiro's pure goodwill leaves Giyuu with nothing to say. He stares at his feet as they tread the road, letting his hair fall down to hide his face. How can an eldest child think of Giyuu like that? Let alone an eldest child like Tanjiro, who has dedicated so much impossible effort to his younger sister's well-being, who has carried on his family's memory so gracefully.
Giyuu has never once succeeded at protecting or supporting another person.
Tanjiro seems to take no issue with his lack of response, tilting his head back to gaze into the sky, a soft smile curling his mouth.
A thin, razor guilt wraps tight around Giyuu's chest, squeezing his lungs. Somehow, he's made Tanjiro think he's something he isn't, but… To have a younger brother like Tanjiro would be an honor. He has no doubt.
— burning tears well up in his eyes, spilling over before he can even try to stop them.
Giyuu's legs give and he collapses to his knees, the bruising impact sending a shock through his wrung-out body. His ears ring. His severed arm aches. He can still feel what isn't there anymore, every inch of pain, every pulse of the opened arteries soaking blood into his bandages.
All of it is snuffed out by the knowledge, ice-cold in his chest, that he failed. Again, he failed and lost something precious that he can never get back.
They managed to survive the Infinity Castle, they defeated an Upper Moon, they killed the King of Demons, and Giyuu would've carried Tanjiro on his back with the last of his strength the rest of the way. He would've gone to hell to keep Tanjiro here, to return him to Nezuko, if he'd only found the opportunity.
Giyuu can never find a way to trade places with the people who deserve life more than he does.
The thought that he could've been like an older brother to the Kamados is laughable now. Someone like him…
"Forgive me," he whispers, laying his hand over Tanjiro's, palm covering knuckles locked in a dead grip around a broken sword. "I'm sorry, Nezuko."
Giyuu closes his eyes, pushing more tears down the bridge of his nose.
"I'm so sorry."