Ōmagatoki

Ōmagatoki (逢魔時 and 大禍時, lit. "Time [of] Rendezvous [with] Evil Spirits/Demons" and "Time [of] Great Calamity") – a Japanese term referring to the moment at Tasogare (昏, lit. "Dusk", "Sunset", "Twilight"), when the sky grows dark. The opposite of Tasogare is Akatsuki (暁, lit. "Dawn", "Sunrise", "Daybreak"), Ōmagatoki has specific meanings for the two ways of writing it: first, "the time of meeting Yōkai, Yūrei, and other-such dark creatures"; and second, "the Time of Great Calamity".

Ōmagatoki as depicted by Toriyama Sekien

In Illustrated One Hundred Demons from the Present and the Past, Toriyama Sekien described Ōmagatoki is the time when Chimimōryō, the evil spirits of the mountains and rivers, attempt to materialize in the World of the Living.