The Sky Is Full of Stars, Frost and Snow

Because of an unexpected encounter, Xingchen and Shuangxue tied a slender red thread. The thickness of the thread constantly changes with the relationship between the two of them. When it is far away, it is very thin and seems to be broken at any time. When it is close, it is thick and cannot be broken no matter what. The depth of the relationship becomes less important over time. Later, the protagonist's question gave the answer. The red thread has a name, called - love.