Zi (子) — Rat Branch / Yin Water

Zi opens the twelve-branch cycle and corresponds to the depth of midnight, the depth of winter, and the cardinal North. Its hidden stem is 癸 (yin water) alone — making Zi the purest expression of subterranean, quietly intelligent water. People with Zi prominent in their chart often act in the small hours, think in private before announcing, and find truths others miss in the dark.

Zi forms the san-he (three-harmony) wood frame with 申 and 辰 (申子辰合化水), and the liu-he (six union) with 丑 (子丑合土). It is conflicted by 午 (子午相冲) — the noon vs. midnight axis, the most direct opposition in the zodiac — and harmed by 卯 (子卯相刑).