Under Zhang Tie's control, the master-level Mirror Clone Technique rune, wrapped in the spiritual energy Yan Feiqing had poured into Zhang Tie's body, sank from the void of the Sea of Consciousness into the void of the qi sea. It revolved beside that black-hole-like mass of energy brought by the Thunder of Annihilation, absorbing Yan Feiqing's spiritual energy on one side while, like a magnet, competing with the black-hole energy in Zhang Tie's qi sea for the Battle Qi generated there. Nourished by both spiritual energy and Battle Qi, that miraculous Divine Rune gradually filled out, blazing with golden light...
Spiritual energy was like water. As long as one did not deliberately control it or employ certain secret arts, entering another person's body would generally bring no negative effects. Battle Qi, however, was like fire. Apart from the Battle Qi of a few cultivation arts that could nourish others when sent into their bodies—for instance, the supportive water-and-wood Battle Qi cultivated by the sisters Ai Mei and Ai Xue, which could help Zhang Tie recover and massage his body without causing harm—the vast majority of Battle Qi would inflict tremendous damage upon entering another person's body, like firing a bullet into them or making a volcano erupt within them.
Even Zhang Tie, at a time like this, did not dare let Yan Feiqing pour her Battle Qi into his body to activate the Divine Rune of the clone technique, because that would basically be suicide.
By the same token, allowing highly destructive Battle Qi into the fragile, sensitive void of the Sea of Consciousness in the brain was equally dangerous. Under normal circumstances, the spiritual energy within the Sea of Consciousness could sink into every part of the body without causing any side effects, and nourishing certain special areas with