If his father's fury is a sound, it's the roar of flames and the roar of shouting and the roar of the crowds watching his villain fights like an old Roman colosseum, hungry for the carnage before them.
If his mother's fury is a sound, it's a whistle. The whistle of breath between clenched teeth and the whistle of a tea kettle boiling and the whistle of the wind through an empty, lonely house.
(He'd thought, once, that his fury was the sound of silence. The silence of breath held so he wouldn't be found, the silence of fear and impotent, smoke-tinged resentment when there was nothing else left.)
If his classmate's fury is a sound, it's thunder. Loud. Light and lightning, flash and heat and booming, dangerous anger, sweet sugar burned black and bitter.
If his best friend's fury is a sound, it's percussion. The percussion of walls of ice falling falling falling. The percussion of broken bones and broken perceptions, the heavy thump of hearts beating wild in chests. (It's the percussion of hands hitting a school desk and a flinch in response.)
Shouto finds his own fury sounds like none of those.
If his fury is a sound, it's the dull thud of impact, the wuff of kindling catching alight, ignition. It's the crunch of snow underfoot, the ice-crackle of a glacier under pressure cracking cracking cracking until, with a sound like glass wind chimes, it shatters.
If Shouto's fury is a sound, it's—
"Leave him alone!"