The fruit of the Amakumo Grass, which grows on Seirai Island. You can hear it crackling with a tiny current if you hold it up to your ear.
The Amakumo Grass was born when the terrible slaughter that tore through Seirai Island, causing it to ever be under a stormy shroud, ended. As if showing its defiance, it will bear fruit while facing the peals of thunder from the sky.
This bold spirit also accompanied those who emigrated to Seirai Island, until Koseki Village was at last ruined and no clergy-person was left to man the Asase Shrine.