They are just little stories about them, to show more of their personalities. If you read the novel, you'll understand. In this chapter, little theater story was set up when Xu sheng was in first year class 1, he had a lot of female friends Because he was good at colour matching and stuff. Author add these little stories according to chapter elements. Like we saw that girl in ponytail who came to see Xu sheng, that's why they added this story to show that Xu sheng was famous with girls but not for a certain reason. And because of this he got named as xu •friend of women• sheng. I hope you understand now,
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Yeah, I know what they are and it feels messy
I get it but wtf little theatres