甲子 Day Pillar (Jia Zi): Na Yin and elements
What the Day Pillar shows
The 甲子 (Jia Zi) Day Pillar pairs the Yang Wood Heavenly Stem with the Rat Earthly Branch. In a full chart this is the pillar readers use to locate the Day Master — the reference point from which other stems and branches are compared.
The Na Yin image
In the Na Yin tradition, the 甲子 pair carries the image "Metal in the Sea" (海中金, Hai Zhong Jin). Na Yin is a poetic layer that assigns a combined image to each consecutive pair of pillars. It is a traditional vocabulary for noticing quality and texture, not a prediction.
How the stem and branch interact
The stem is Yang Wood (Wood) and the branch is associated with Water; in this pairing, the stem element feeds the branch element. Traditional readers describe this configuration as a mixed structure that depends on the rest of the chart.
A careful reading boundary
A Day Pillar is a calculated position inside a Four Pillars chart, not a verdict about a person. Read it with the Month Pillar, the visible elements, and the certainty of the birth record.