Dangerous Seed © 1989 Namco.
The player assumes control of three separate ships. Each ship has a different firing pattern. When the three ships are combined together, they form the Moon Diver. Their mission is to quell an alien invasion which is spanning all of the Milky Way and destroy the alien headquarters: the Danger-Seed.
The player starts the game with three separate fighters and has to make it through four tubes using the fighters separately. If one gets destroyed, then the next, more powerful ship makes an attempt to get through. If the player makes it to the fifth stage, the three ships combine into a singular composite ship called the "Moon Diver", which has a massive amount of firepower.
Click to enlarge