Maybe calling like this, as an elder, might seem close.
He's the younger brother, a generation younger than Su Qianqian, calling like this is somewhat disrespectful.
This also shows the low status Su Qianqian has in this family. Su Jun is already used to this sense of superiority, so he can call Su Qianqian by her nickname without feeling awkward.
Su Jun's girlfriend felt somewhat inferior when she saw the beautiful, fairy-like, noble and elegant Su Qianqian.
"Su Jun, is this your girlfriend? Aren't you going to introduce her to your sister?"
Su Qianqian saw the other's shyness and proactively asked.
"Her name is Yan Yan, she's a nurse in the city. We've been together for almost two years now, and we're planning to marry this year."
"Hello, beautiful Yan! I really admire nurses because every time I go to the hospital, it's the nurses who give me injections and change my medicine. They are always so approachable whenever I have questions."
