Tengu tsubute

Tengu tsubute (Japanese: 天狗礫 or てんぐつぶて, meaning "a stone thrown by a tengu") is a phenomenon where rocks mysteriously fall from the sky in Japanese mythology. It is most commonly encountered deep in the mountains, however tales of rocks mysteriously falling from the sky are found in larger cities as well.

Myths & Legends
People who are struck by tengu tsubute usually fall ill soon afterwards. Even those who merely witness this phenomenon often suffer misfortune: hunters will not be able to find their prey, fishers will have a poor catch, and so on. Stranger yet, the rocks are often invisible. After they fall to the ground, no rock can be seen where one should have fallen. When they hit water, ripples and a splash occur even though no rock is seen. And no matter how hard a person is struck by a tengu tsubute, no wound or mark is left on the body.

Appearance
It usually takes the form of a handful of pebbles or gravel flying through the air on an evil wind, however from time to even even boulders are blown about in this way.

Origin
Because these rocks fly as if thrown from seemingly nowhere, this phenomenon is believed to be the work of tengu (or other yōkai—occasionally mischievous kitsune and tanuki are blamed as well). Because tengu hate the wickedness they see in humans, it is believed they throw rocks in this way to punish the unrepentant and to remind us to behave.