Vertical shoot-em-up ported from the Naomi Arcade version. Ikaruga is more or less a sequel to Radiant Silvergun on the Sega Saturn.
Based on a two-colors system, the player has to switch between the black & white sides of his ship during gameplay.
The black side is immune to black enemy bullets which it considers as a bonus and dies on impact with white enemy bullets. Your own black bullets damage white enemies twice as much as white bullets. And vice-versa for the white side. Those properties make a balance between protecting yourself well and killing enemies fast.
This aspect, combined with specific enemy patterns and a combo system makes Ikaruga an original shoot-em-up with a dose of strategy.