Xu is the yang-earth branch (hidden Wu, Xin, Ding), the 9th month, 7–9 pm — the Fire vault, dry earth that guards.
Xu is the Fire vault, the driest earth. Friction: the Chen–Xu clash, the Chou–Xu–Wei punishment and You–Xu harm; warmth: Mao–Xu harmony and the Yin–Wu–Xu fire frame. Xu gives its whole heart — but its loyalty must be paid in loyalty.