The infamous Red Capsule is an essential powerup in the Gradius Series, Nemesis Series, and Parodius Series. It has been mimicked in many games that use a powerup system similar in style to the aforementioned games. Essentially, the Red Capsule allows the player to gain access to the available powerups by incrementing the weapon bar choose space by one.
This item is so important that it was used as a boss in several Parodius games and is called Capsule Monster Cappuccino. It's main method of attack is to shoot many streams and bursts of Red Capsules with the occasional red spiked shot to trick the player.