Ikaruga is a vertical-scroll, shoot'em up video game developed by Treasure, originally for the Sega NAOMI in 2001.
Like Radiant Silvergun, it is a shooter game. The difference is that it handles the concept of switching polarity. The player ship can change between black and white, and fires shots that match its current polarity. All of the enemies are either black or white, and hitting enemies with their opposite color does additional damage. The player ship can absorb same-colored enemy fire, and absorbing shots charges a secondary attack. There are three difficulty levels.
On "Normal", enemies that match the player's ship's color release a burst of same-colored shots when destroyed. On "Hard" all destroyed enemies release a burst of shots in their color, and on "Easy" none of the enemies release any shots when destroyed. Despite their names, "Easy" and "Normal" modes can actually make the game more difficult in certain situations, because they reduce the number of dots that a player can absorb to charge their screen-clearing special attack.
Like many bullet-hell shooters, the hitbox for the player's ship in Ikaruga does not encompass the player's entire ship and only exists at the ship's exact center. If an enemy projectile or ship makes contact with the center of player's ship, they lose a life. On each playthrough a player has three lives. Once these lives are depleted they must use a Continue if they wish to keep playing.