Then you haven't completed someone's quest line. It's usually Elsa or Annie's branches that people miss. Check those
See that's the thing I've gone as far as the game will let me with every character except mikasa she is only at the training grounds at morning during the day its just Annie and Sasha there. I can do the mini game with Annie but I can't seem to beat to I have to to unlock mikasa so I can train with her?