How do you get stars in dragonball raging blast

you first go to the story mode place then you have go to a battle you already completed and you can do missions that will earn you stars, and i think all of them have a mission that you have to complete it in hard difficulty then when you get some there will be a section like the saiyan saga and buu saga called the star shop where you can spend it on costumes and battles and you can even get the best super saiyan tree battle where you can unlock vegeta super saiyan three