Tsubaki's problem is that she is too passive and is the type of person who is afraid to voice her own opinions from what I can see. This was why her brother thought she was pitying him because she was always so "nice" to follow him even though she holds a lot of talent. But that is just her personality and I don't want to see that changing honestly
This was a whole misunderstanding and it was just unfortunate that her brother fell prey to the dark side.