This is the first entry in what will be an irregular series of posts on myth and folk lore from classical Japan. Any game mechanics referenced in the post are for a modified version of the King Arthur Pendragon RPG I've been working on for Nocturnal (publishing date still TBD), but the details should be easily adapted to any system of your choice.
During the reign of Emperor Saga, a scorned wife journeyed to the Kibune Shrine on the northern outskirts of the great capital of Heian-kyo. There, during the Hour of the Ox (1:00-3:00 AM) when the boundary between the material and spirit worlds is thinnest, she prayed to the gods of the shrine, beseeching them for vengeance upon the man who had left her. She returned at the same time every night, seven nights in total.
The gods heard her prayer and directed her to don lit candles upon her head, cover herself in poisonous cinnabar, and lay down in the Uji River. The woman did as instructed, and after 21 days she became something more than human, a vengeful spirit called Hashihime ("Maiden of the Bridge").
Despite the fact that Hashihime was ultimately foiled in her attempts to kill her husband thanks to the intercession of the great wizard Abe no Seimei, her legend inspired scores of other jilted lovers to follow her lead.
The Ushi no Koku Mairi Ritual
This is perhaps Nihon's most notorious black magic ritual. To enact the ritual, gather a bundle of straw and shape it into a roughly humanoid form. Don a white kimono, cover your face with white paint or powder, then hang a mirror around your neck. Wash your hair and place the tri-pronged stand of a gotuku (iron brazier) atop your head. Stick a candle on each prong and light the wicks. Slip on a pair of geta (wooden sandals). Clench a comb in your mouth.
Taking a mallet and some iron nails with you, run from your residence to the nearest shrine that accepts curses. (In Heian-kyo, this is usually the Kifune or Jishu-jinja Shrine.) Find a tree on the property of the shrine and wait until the Hour of the Ox. Nail the straw doll to the tree while uttering salty curses against the target of your ire.
Repeat this ritual for six more nights. By the final night, the doll will have seven nails in it. Placement of the nails will determine what sort of ailments the target will develop: nails in the arm might indicate a broken humerus bone, a sprained wrist, a burn in that location, and so forth. A nail driven into the head of the doll will cause death!
If anyone sees you enacting the ritual and lives to tell the tale, the curse will rebound onto you, so make sure your nighttime visits go undetected, or else be prepared to use that dagger you thoughtfully tucked up into the sleeve of your kimono…
In order to undertake this ritual, you must possess a Kirai (Hate) passion directed at the target of the ritual. At the end of the seven-day period, roll against Kirai. With a critical success, your intended injuries affect the target. The most minor injury will occur 1D6 days after the ritual concludes; each successive injury occurs 1D6 days after the preceding wound. Wounds should cause a progressive amount of damage: 1D6 Hit Points for the first, all the way up to 7D6 for the final.
Characters may be driven to try this ritual due to madness caused by a fumbled passion roll. More usually, of course, player characters will find themselves targets of the Ushi no Koku Mairi ritual! At the Gamemaster's discretion, it may be possible to halt the progression of injuries caused by the ritual by consulting a powerful yamabushi or tengu and beseeching them to lift the curse before it is too late.