BS-06 is the penultimate boss from Raiden III.
Details[]
This boss is a spaceship with two large cannons on it's sides. During the first phase of the battle, it will release indestructible green spheres (like the ones which litter the stage), making the fight much tougher, all while shooting at the player. After taking enough damage it will drop the cannons and open it's wings to continue the fight, shooting much thicker bullet spreads.