Dead or Alive 5

To earn this secret achievement that's called "And Then THIS Happened!", you will need to clear all the chapters in Story mode.

That's all you have to do really. You can do the bonus missions to gain titles along the way (which is what I suggest you do so that you can earn them towards getting Alpha-152), but you don't really have to. All you have to do is beat your opponent in each fight and watch the story as it unfolds (which is something else I also recommend to do for another achievement called Insomanic). The achievement doesn't unlock until after the credits are finished rolling on the screen and when you'll hear some dialogue between two people. When the next screen, after the credits are done, comes up and the dialogue begins, the achievement should unlock.

Have fun and good luck!