hyakki yagyou

百鬼夜行 (Hyakki Yagyou or Hyakki Yakou, literally "Night Parade of a Hundred Demons")

This tag is possibly ambiguous.

For a horde of traditional youkai in the Japanese folklore, demon_parade tag is currently used.

For an unofficial series name of Toriyama Sekien's Youkai Encyclopedia tetralogy, just use nihonga tag, or use Gazu_Hyakki_Yagyou.

For a novel series by Kyougoku Natsuhiko, use Hyakki_Yakou_(Kyougoku_Natsuhiko). Its pixiv tag is 百鬼夜行シリーズ

For a PSP game, use hyakki_yakou_~kaidan_romance~. Its pixiv tag is 百鬼夜行～怪談ロマンス～