Bangai-O Spirits doesn't have a story to speak of; the game's tutorial is a fun interchange between a random anime scientist and his two assistants who pilot the mech. But besides the 17 levels that are designed to teach you how to perform all of the attacks and movement controls, the game simply lets you play any level on the cartridge, in any order.
The list of levels is divided into four categories. First, there is Treasure's Best, which is 27 levels created by the developers at Treasure. The Puzzle Stages are just as you would expect, a series of levels that can't be beaten by simply blasting away. Other Stages consists of the rest of the game's included levels, while the Custom option lets you load up any of the levels you either created or downloaded via the Sound Load feature.
Besides the two modes that let you actually play various levels (Tutorial and Free Play), you can also choose Edit Mode that lets you either start a new level from scratch or build one based on any of the other levels found in Free Play mode. Interestingly enough, this mode can be entered into while in the middle of any stage simply by tapping the (Select) button. I find the game's Edit mode to be one of the more interesting aspects of Bangai-O Spirits, but we'll talk about that more in the Game Mechanics section.
The last option is Sound Load which lets you prepare your game to accept a custom made level from another copy of the game. Instead of requiring some sort of wi-fi link up with another game, you simply have to go to Sound Load and either let your DS listen to your friend's level, or choose a level that you want to share. The result is a series of high-pitched screeches that anyone whose ever used a dial-up internet connection will remember. Provided the transfer is complete (I only had minor issues, and those were typically from levels I loaded off of YouTube or other websites), you will then have a copy of your friend's level to play or edit to your heart's content.
