If it is a young girl named brother, it must be partly because she has a good impression! Because girls in youth are all brothers and sisters, and even deepen their ambiguity. Otherwise, there are so many names, why do you have to call that boring brother? It is because girls are shy to be closer to you, but things like baby and dear are too straightforward to call, so they can only express their affection for the opposite sex by calling "brother". If you don't like yourself, you can call Tiezi, brother, buddy, hello.
If it is that kind of working relationship, I mostly want to get closer to each other as soon as possible, so that it is more convenient to do things in the future. For example, in the workplace, addressing seniors is generally called elder brother or elder sister, which can not only bring the relationship closer quickly, but also show respect for seniors. When you want to ask your seniors something, you can call me at the beginning, which makes it easier.
Of course, the possibility of their relationship being open is not ruled out. Because sometimes someone wants to get close to you, and you are disgusted and can't refuse it to your face. You can call me brother and then add a sister-in-law at the back, which will be effective. This kind of address is generally aimed at some people who have families and want to take advantage of the little girl, just to show their respect for him and to refuse him.
The other is ... pure blood relationship, so it's called brother.