You obtain this achievement automatically after you finish the 11th chapter called "Last leaf"Note:
If you play the first time chapter 11 then you play automatically chapter 12 / epilogue called "Renewed" too. After you complete the game, you can select both in the main menu (chapter 12 is directly beside the chapter 11 picture, it is the Flowerpot)
Chapter 11 has no collectibles or misc. achievement. Chapter 12 has 5 secrets and the flow achievement.
In the spoiler you find a complete video walkthrough of chapter 11!