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It's nearly silent in the butterfly estate. Everyone else has long gone to sleep, and Zenitsu cannot stop being afraid.
Zenitsu is very familiar with fear. Most of the time it crashes down, all consuming and unrelenting. It leaves him yelling and crying until he can't take it and his body gives out. And for a few blissful hours afterwards, he can feel nothing.
But sometimes, the fear is more subtle. Sometimes it's a swirling pressure in his chest that slowly grows and makes his heart pound. It climbs up to his throat and makes it harder to breathe. It settles behind his eyes and makes his head hurt and his eyes water. It runs around wild in his head, and forces him to think of awful things.
This is the fear that takes hold of him tonight.
He thinks about his friends in the beds right across the room, and he thinks what if they hadn't made it back from that latest demon attack. Zenitsu was used to worrying about his own mortality. He was faced with it so often these days. But now, realizes, that the only thing that scares him more than his own death, would be the death of the people he cares for. He knows he can hardly protect himself. He knows he's weak, and that he should have died a long time ago, but for some reason he hasn't. (And gods, sometimes he wished it would just happen already so he could stop worrying about when-) But what happens, when that weakness is the difference between someone else living and dying?
He thinks of Inosuke and Tanjiro's bodies, broken and still. He thinks of the merciless demons, and how they wouldn't hesitate to devour those bodies when given the chance. He thinks about how neither of them hesitate, never stop to think about their own lives. (Why don't they ever hesitate? Don't they care about their own lives? Don't they know he can't do this alone?)
He thinks of screaming and blood and sharp teeth. He thinks of his own helplessness, and about how he'd be powerless to help the people who have helped him more than he could express. He thinks of being alone. And he thinks that it would be his fault.
He thinks of his friends, dead.
He thinks of his friends dead, and it's his fault.
Zenitsu thinks, and he thinks, and he thinks until his brain is on fire and tears run quietly down his face. Until he's biting his lip so hard trying not to sob, that it starts to bleed. Until he's rocking, back and forth and some poor attempt to comfort himself. Until he's sitting with his eyes closed, to concentrate on Tanjiro and Inosuke's breathing.
He counts each one, to know that they're still alive.
Everyone else has long gone to sleep in the butterfly estate, and Zenitsu does not think he'll ever stop being afraid.