He Shutong practices the Ice Heart Skill, which, once mastered, cannot be changed. However, she wishes to learn the Yuan Sword, so naturally, she understands the various Heart Method texts of the Heaven and Earth Yin Yang Joy Sect.
The Joyful Union Skill is named as a Dual Cultivation Skill, but it discusses the Dao through Yin and Yang, which actually aligns with many great cultivators' viewpoints. However, the 'Yin and Yang' here has a distinct reference: Yin is the Yin within Li, referring to female Yin essence; Yang is the Yang within Kan, referring to male Yang essence.
In the eyes of the founder of the Joyful Union Skill - Yin and Yang in harmony, continually creating life. If one is missing, all things will not come into being.
The first half of the sentence speaks of the powerful dual cultivation effect brought by the cooperation of Yin and Yang, while the latter half speaks of the harm caused by the absence of Yin or Yang.
