When I was collecting the material, in order to start working with the image of kitsune, I could not even think that this is such a controversial youkai.
This illustration shows a kitsune wedding, during which foxes light up the lights. Soaring lights are called kitsune-bi in Japan, literally "foxfire". It is believed that the kitsune produce these bluish lights with their breath or, sometimes, with their tails. If the fire is bright, the farmers believed that the harvest this year will be good.
Usually, the lights are seen in winter. Sometimes horse bones were found in the places where they were seen. From this comes a fairly common belief that the kitsune keep lit horse bones in their mouths, which is this foxfire.