Kingdom Hearts - Birth by Sleep (PSP) - Help

I have finished all 3 character stories on critical. so what do i have to do to get the secret ending? and is their more than 3 characters to play?

 

You get the final chapter after you collect all the reports. Apparently a lot of people miss the one in Terra's story. You get it after you advance far enough in Mirage Arena. After you have all the reports, just finish the game like you normally would and you should unlock the final chapter.

And no, you can only play as the three main characters.

 

So all together how many reports are there?

 

There are 12.

 

And after you complete that, there are some side bosses that become available on terra and ven's stories.