Fire sits at the peak of the Wu Xing cycle, the phase of greatest expansion before the turn back inward. In the generative, or Sheng, order Wood feeds Fire, as fuel feeds a flame, and Fire in turn feeds Earth, its ash enriching the ground. In the controlling, or Ke, order Fire controls Metal, melting it, while Fire is itself controlled by Water, which extinguishes it. The two cycles run at once in any reading of a person or a season, and a practitioner is trained to ask which relationship has slipped rather than which single phase is to blame.
In Chinese medicine Fire governs the Heart and its paired Small Intestine, and by extension the tongue, the blood vessels, and the capacity for joy; an excess is read as Fire blazing unchecked, a deficiency as a flame gone cold, both disturbing sleep and speech, which the classical sources place under the Heart's charge. Fire's season is summer, its direction south, and its colour red, correspondences carried into ritual timing and into the placement of red and pointed, upward forms in feng shui practice.
The generative and controlling relationships are also the diagnostic backbone of five-phase acupuncture: a practitioner treats not Fire alone but the phase feeding it, controlling it, or drained by its own excess, a systemic logic that distinguishes the Wu Xing from a simple list of five correspondences.
Sources Science and Civilisation in China, Volume 2: History of Scientific ThoughtJoseph Needham with Huangdi Neijing (The Yellow Emperor's Inner Classic)Traditionally attributed to Huangdi; actual authorship unknown