Getting achievements for warriors orochi 2 do i HAVE TO DO STORY MODE?

Now i am getting all the achievements for Warriors Orochi 2 and i am trying to do all the story mode levels. Now my question is do i have to do story mode? Or can i do free mode? That seems to be a lot better. I have finished Shu, Wu and Samurai story lines and half way with Wei. So can I do free mode? Or does it have to be story mode?