Japanese Era Calendar (元号 Nengō) (日本年號)

THE JAPANESE ERA CALENDAR (元号 nengō) — the reckoning on every Japanese official document, licence and coin: years counted within named imperial eras, and 2026 is REIWA 8 (令和8年). DAY-EXACT, GAZETTE-CLASS: the statutory boundaries of the Gregorian period served precisely — Taishō from 30 July 1912, Shōwa from 25 December 1926, Heisei from 8 JANUARY 1989 (the first seven days of 1989 are Shōwa 64, the famous seven-day year), Reiwa from 1 MAY 2019 (the abdication era: 2019 splits Heisei 31 / Reiwa 元年) — every boundary ASSERTED AT LOAD on both sides, the Reiwa 8 = 2026 anchor pinned, and the era-year arithmetic round-tripped across the whole served range. Converts BOTH ways: any date → era, year, and the formatted 令和8年 / R8 forms (year 1 correctly written 元年 gannen); or era + year → Gregorian, with nonexistent combinations (Taishō 20) refused by name. Era-name glosses are the standard published translations — Reiwa's 'beautiful harmony' is the official one, the first era name drawn from Japanese rather than Chinese classics. DEFERRED BY NAME: dates before 1 January 1873 (Japan's civil calendar before the Meiji 6 reform was lunisolar — Meiji 5 ended 2 December 1872 and the NEXT DAY was 1 January 1873) and the 200+ historical nengō with mid-year lunar boundaries — refused, never approximated. Japanese becomes seventeen systems. Pure compute, no LLM.

Cost: 1 TIAN Points per call. tRPC procedure nengo.convert.