Lu Zhou has had more sisters than others since he was born.
Benai is two years older than him, so he can call her Sister Nai politely.
Xu Xiying is one year older than him, and he can call her "Sister Xiying" like a gentleman.
Only Qi Yuan, who is half a year older than him, obediently calls him "sister"
The key point was that Qi Yuan felt that when Lu Zhou called her sister, his tone and eyes were a bit evil.
The medical sister who is cool and cold but actually good at embarrassment and cowardice, and the scheming, all-powerful little wolf-dog brother