Tenichijin (天一神・方違え) (天一神方位)

天一神 (Nakagami) and 方違え — the Heian court's directional-taboo cycle, the onmyōdō layer that made Genji monogatari's aristocrats lodge overnight at a friend's house just to approach their destination from a permitted bearing. The rotation is a fixed 60-day ring keyed to the sexagenary days, and THE TABLE PROVES ITSELF: from 己酉, 44 days through the eight directions (艮6・卯5・巽6・午5・坤6・酉5・乾6・子5 — each segment's ganzhi start plus its length lands exactly on the next segment's start), then from 癸巳 the sixteen-day 天一天上 when the deity is in heaven and every direction is free (while 日遊神 keeps to the house — kept clean for the guest) — 44 + 16 = 60, all asserted at load so a transcription error refuses to boot. Any civil date returns the deity's station (or the heaven period with its day count), the 方忌み taboo bearing, days until the next move, and the katatagae custom explained. Day pillars from lunar-javascript; a 60-day periodicity law and a full-cycle coverage law (16 heaven days + each direction exactly its stay) verified in tests. Distinct from Nine Star Ki (kigaku.directions) and the static 鬼門 — this is the CLASSICAL rotating taboo. Heian cultural history served for reference and literature — not travel advice. Pure computation, no LLM.

Cost: 2 TIAN Points per call. tRPC procedure tenichijin.direction.