the options for replaying the game at a higher difficulty setting. Full story mode The "full story mode" is a single player mode that features a story-based campaign and ship customization. The story is told through the message cubes that can be collected within and read between levels. Some of these messages cubes are readily available while others need to be obtained by destroying certain enemies in the preceding level. At certain points in the game, the storyline branches and the player is required to pick one branch. The player's craft is customizable. It can accommodate a front weapon and a rear weapon. Shops can supply a variety of kinetic guns, rayguns, missiles, and bombs for these two slots. While the front weapons are mostly limited to forward arcs, "rear" weapons often come with wider coverage including side and rear shots. Some rear weapons have two selectable fire modes, focusing either mostly forward, or mostly sideways or rearward. Weapons can be upgraded up to 10 times. Higher levels cost exponentially more and require a more powerful generator to support them. Other upgrades include increased shields, more powerful generators to allow for stronger weapons and shields, more armor, and higher maneuverability. Shop differ in terms of the ships, generators, and weapons that have for sale. However, shops can upgrade any component, even those that they don't sell. The player can also purchase up to two "sidekicks" which fly alongside the ship. Some simply act as a complementary weapon that fire whenever the ship fires; others are powerful weapons with limited ammunition that need to manually activated. Sidekicks may not be upgradable. Arcade mode In arcade mode, the player starts with a moderate ship and picks up the front guns, rear guns, and sidekicks along the way, instead of purchasing them. Front weapons are upgraded by picking up purple bubbles from destroyed enemies. The number of purple orbs required increases exponentially to advance to higher power levels. Front and rear guns can also be upgraded to the next level by picking up power-up pods, which are found by destroying a specific enemy. The ship, shields, and generators are not upgradeable. The arcade mode can be played with one or two ships, by one or two players. The ships are called the "Dragonhead" and "Dragonwing". Both players can combine their ships into one, forming the "Steel Dragon", with the first player controlling the