For Mika, every meet with her, there will be some choice that will add your stat or not, you can try to chosee one and rollback if that choice isn't the right one. For Ryuko, it's more complicated, you can read the detail of the character on character list, what she like and dislikes. That will help you choose the choice... When you get the right stat, ryuko will ask you to come to her bedroom.