Sorry, I do not correctly understand the essence of your question.
If you use the interface, then you must specify Tatget object to which you want to address (in your case to pass a variable).
Judging by the first screenshot, you try to cast on Character (but the object casting is not specified), then at the interface message in Tatget which nothing comes (cast fail,try to debug it).
But how controller knows which of the character currently selected?
You must clearly indicate the object to which the message is transmitted.
Try to collect it in your own controller.
But with this approach, variable will change in all characters inherited from Character.h