Ilgan
The protagonist of BaZi — the heavenly energy that represents 'you'
The Day Stem (日干, Ilgan) is the Heavenly Stem of your birth day in BaZi. It represents 'you' — the self — and serves as the reference point for all analysis.
BaZi (Four Pillars) consists of four pillars — Year, Month, Day, and Hour — each formed by a Heavenly Stem and an Earthly Branch. The Heavenly Stem of the Day pillar is called the Day Stem. It symbolizes your core energy, personality, and 'self' in the entire BaZi chart.
Day Stems are divided into 10 types based on the Yin/Yang of the Five Elements: Jia (Yang Wood), Yi (Yin Wood), Bing (Yang Fire), Ding (Yin Fire), Wu (Yang Earth), Ji (Yin Earth), Geng (Yang Metal), Xin (Yin Metal), Ren (Yang Water), Gui (Yin Water). Each carries unique character energy — Jia like a towering tree, Ding like a gentle candle flame.
The Day Stem is a single character (the Heavenly Stem), while the Day Pillar combines both the Heavenly Stem and Earthly Branch. For example, in the Jia-Zi (甲子) Day Pillar, the Day Stem is 'Jia'. The stem reveals your core nature; the pillar shows how that nature interacts with its environment.
Every core concept in BaZi — Ten Gods, strength/weakness, and useful elements — is calculated relative to the Day Stem. Whether other elements support, control, or weaken you is always judged from the Day Stem's perspective.