Order of Ecclesia/Blue Chests< Order of Ecclesia
There are two categories of Blue Chests: hidden ones that you can find by pressing the down button on certain spots and others that are given to you for an achievement (mainly beating Bosses without receiving damage). Click on the link to go to the relevant walkthrough section (your browser's search function can also help).
Each Boss (other than Jiang Shi) leaves behind a Blue Chest with a medal if you beat them without receiving damage. For Dracula's medal reload the save file after you've beat him.