Let's talk about WeChat routine.

Hello, my friend. Well, the girl calls you little brother on WeChat, so just call her little sister! After all, China has always advocated reciprocity since ancient times.

Well, if this girl is your friend and her classmates usually play high, it doesn't matter what she calls her. Nothing special, more lively, but if she just met you, of course, she should behave more solemnly and leave a good impression on others, otherwise others will think you are a slacker.