乙 Yi
Yin Wood, the vine, the grass, the flowering creeper. Soft, adaptive, and far harder to kill than anything rigid.
What a Yi day master is
Yin Wood grows sideways, around obstacles, using whatever structure is available. Where Jia stands, Yi climbs. This is the most survivable of the ten stems: it accommodates, it endures, and it is still there long after stronger-looking things have gone.
In Chinese astrology your core element is Yin Wood, pictured as the vine. You are flexible and persistent, growing around obstacles instead of through them. You survive what breaks harder things.
Yi at its best, and where it strains
Strength. Adaptability without loss of direction. Yi gets where it was going by a route nobody expected.
Difficulty. The vine needs something to climb. Yi can become dependent on a person or a structure, and mistake the trellis for its own strength.
Yi shares its element with Jia, the yang form of Wood, and the two behave nothing alike. That is the whole reason BaZi uses ten stems rather than five.
The four relationships every BaZi reading runs on
Your day master is not read alone. Everything else in the chart is judged by how it treats Wood, and the five elements move in two cycles: one that nourishes and one that restrains. For a Wood day master those come out as follows.
A chart with plenty of Water and little Metal reads very differently from the reverse, even with the same day master. That balance is what a BaZi practitioner is actually looking at, and it is why two Yi people can be unrecognisable to each other.
BaZi pillars here use the solar calendar the tradition uses, so the year turns at Lichun in early February rather than at the lunar new year, and the hour pillar follows the late-Zi convention.