Sesshō-seki, Volcanic rock in Nasu, Japan.

Sesshō-seki is a volcanic rock at Mount Nasu in Tochigi Prefecture that continuously releases toxic gases and keeps the surrounding landscape bare and lifeless. The stone sits in a steaming area where sulfur dioxide rises from cracks in the ground and creates a gray, inhospitable setting.

The legend spread during the Heian period when an imperial warrior defeated a fox spirit that supposedly turned into this deadly stone. Buddhist monks later tried to break the curse by shattering the surface into smaller pieces.

The name sesshō derives from a Buddhist precept meaning to take life, given because volcanic gases here killed birds and animals. Each May the Goshinka Festival brings about 100 torchbearers in white robes and fox masks from Nasu Onsen Shrine down to the stone, where a roughly 5-metre torch is lit and the White-faced Golden-haired Nine-tailed Fox Drum is performed.

The area lies near Nasu-yumoto hot springs, where warning signs mark the safe distance from the gas. Visitors should be especially careful when wind comes from the main direction and not stay close for long.

The split was confirmed on 5 March 2022, after cracks had been visible for several years; Nasu Town judged natural weathering the likely cause. On 26 March 2022 the local government had priests hold a ceremony at the broken rock with prayers, offerings and haraegushi wands. In December 2022, eight wild boars were found dead near the stone, the first boars recorded there.