naturalists (as a group) or naturalist (individual), promoting a closer connection with nature (lifestyle, food, etc.)

spontaneous combustion

to spontaneously combust

natural right

fondue pot

match (device to make fire)

Kyūjitai form of 火薬

(Buddhism) a fiery chariot that brings sinners to hell; by extension, a form of torture using this vehicle / a burning fire in the shape of a wheel / Short for 火車婆 (kasha-baba): a powerful, evil old hag

boiler / furnace

(Internet slang) Firefox (web browser)