A derivative work is kind of like a drawing that you make based on another drawing. It's like you looked at the original drawing and then made your own version of it.
In Hong Kong, there is a controversy about derivative works because some people think that it's okay to make them without asking the original artist. They think that if they change the original drawing enough, then it's a new drawing and they don't have to ask permission from the original artist.
But other people think that this is not fair because the original artist worked really hard to make their drawing, and they should be asked if someone wants to make a new version of it. They think that even if you change the original drawing a little bit, it's still the artist's work and they should have a say in how it's used.
So, sometimes people in Hong Kong get into arguments about derivative works because they can't agree on whether it's okay to make them without asking the original artist or not. It's kind of like when you and your friend want to play with the same toy, but you both want to use it in different ways.