他似月亮冰冷无情她似太阳遥不可及
[tā sì yuè liàng bīng lĕng wú qíng tā sì tài yáng yáo bù kĕ jí]
The nickname describes a relationship where one person is cold and distant like the moon, while the other is warm but unattainable like the sun. It reflects feelings of loneliness and separation.