The game is based around an apocalypse. You learn the world is going to end, and you are granted a Book of Prophecy. Long story short, it's your job to go around and document things in the book by slapping them with it, modify them as you please, and then take them to the next world. This book allows for a unique mechanic of modifying items and enemies, and even other characters in the game, letting you customize anything you have documented to your desire. Having trouble with an enemy? Adding some blocks of sickness should lower it's HP. Don't like the look of your sword? Go ahead and unlock a new design for it with one of the puzzles you found. While there are some limits to the customizing, strengthening, and weakening of documented items, the whole idea of getting to custom design the world yourself and the humor of hitting enemies and friends with an invisible book adds some fun to the majority of original RPG concepts.
Outside of it's customability, the game acts much like a normal RPG. There are two basic screens that you can interact with in the game, those for fighting, and those for bond-building. Inside of certain town walls, you cannot fight, but can only speak to, and give gifts to those allies you have befriended. Outside of the walls is where you can fight enemies and gather EXP, through two methods of fighting, the traditional method, and a new method called juggling. In the game, you also have four sprites, attached to the book of prophecy, that you can bond with, and utilize in battle. The four of them are elementalists that can unleash huge attacks on enemies when called upon, which is also how they are bonded to. During the game, you can choose to romance certain characters, or the sprites, a well, unlocking different features as you progress further through the game. I myself chose to romance a sprite, named Ur, which strengthens their attacks and unbinds them from the shackles that they were put in when you originally meet them.
The only downfall of the game is the touchscreen interface, which manages the Book of Prophecy, settings, and all of the customization. It feels clumsy to navigate through, and can be hard to get used to after setting the game aside for a long time. Luckily, just one touch of the book and your game will pause, allowing for any customization to be done to a documented enemy without them attacking you. I didn't have terribly many problems with the interface, but I know some other people have had problems with it.
All in all, Avalon Code is a very well paced, unique experience among action RPG's. It's nearly perfect except for the awkward interface, with well thought out plot elements, characters, and designs. It's one game I sure hope comes out with a sequel in the future, especially if it's something meant for the new graphics of the 3DS.