Xu

The oracle glyph of Xu is a broad-bladed axe (kin to Wu-the-stem, one stroke added) — a weapon at root. The Shuowen: "Xu means extinguishing — in the ninth month Yang qi wanes, all things are complete, and Yang descends into the earth." The ninth month locks the doors; Xu turns the key.

Matched to the Dog — night watch, house guard, loyalty itself — its hidden anatomy is an autumn-night fortress: Wu Earth for walls, Xin Metal for blades, Ding Fire as the single lamp inside. The Fire vault banks exactly this: an ember to cross the winter with.

Xu is the Fire vault — the Yin-Wu-Xu frame banks its blaze here. As dry earth it sides with Wei: damming Water, feeding Fire, and embrittling Metal (parched soil breeds no metal; it makes Xin brittle) — the exact functional opposite of the wet earths Chen and Chou.

In the ninth month Metal recedes and cold has not yet deepened; useful-god decisions often weigh "guard the Ding ember" against "moisten the soil to save the metal." The Xin inside Xu is the jewel half-buried — "Metal entombed in Earth" playing out within a single branch.

Mao-Xu combines into Fire — the spring-wood-meets-autumn-earth match that smolders into flame. Yin-Wu-Xu forms the Fire frame with Xu as vault. Chen versus Xu is the Heaven's Net striking Earth's Net: both great storehouses flung open, Earth quaking on Earth — the classics rank it a structural earthquake, spilling Ding, Gui, Xin and Yi onto the board at once.

Xu holds a corner of the Chou-Xu-Wei punishment; You harms Xu. Its relations run heavy — vaults opening, boards flipping. Facing a Chen-Xu clash or Chou-Xu punishment, inventory the vault contents before pronouncing fortune.

In the pillars Xu computes as Wu Earth, with the Fire vault and Xin residue on file. Fire Day Masters find shelter here — for a fading Bing or Ding, Xu is the winter greenhouse; for a blazing one, the warehouse absorbing surplus flame. One branch, both directions.

To Water it is a parched Seven Killings (Ren dreads the Xu-Wei tandem most); to Metal, a Resource star running dry and brittle; to Wood, a Wealth star banked in the vault. Xu and Hai together are called the Gate of Heaven — in the esoteric tradition, where the horoscope's twelve houses begin: the border post between BaZi and astrology.

The Xu hour (7–9 p.m.) was "dusk watch" — lamps lit, dogs barking: the zodiac Dog's night-watch image fits its hour without a seam. The Xu month brings the Double Ninth festival: climbing heights, chrysanthemums, honoring elders — one last ascent before Yang goes underground.

The characters Xu (戌) and shu (戍, to garrison) differ by a single stroke and share one image: a figure standing guard with a halberd. Watch dog, frontier guard, sealing earth — three readings of Xu, one meaning.