Yun's mother and father died in a battle, and she was never cheerful again. A dream told her that this might not be a coincidence. As she grew older, she no longer pursued this dream which was probably not true. Later, when she met Xun, she became the moon in the darkness...
The change of mood is simply a "dual personality". Sometimes she is ridiculous and sometimes sad. The Gemini Queen (later) seems to be taciturn. She is a sullen person at heart. She seems to know everything. She has great fighting power, but she is willing to be the queen for Shou.
Intention: When encountering bad things, don't be discouraged, maintain a good character and wait for good times