``In the year 5012, the planet known as Abadox is soon eaten by a giant alien organism known as Parasitis. Once the planet has been consumed, the alien takes the form of the entire planet and seeks to devour other planets within the galaxy. The galactic military tries to fight the alien, but to no avail as Parasitis destroys the entire galactic military, except for one hospital ship. It is then discovered that Princess Maria has been devoured as well. The galactic military decides to send out their best fighter, "Second Lieutenant Nazal", to attempt to enter Parasitis' body and rescue Princess Maria before it's too late.
The gameplay largely follows the conventions of side-scrolling shooters of the time. The player shoots down various enemies, all which look like various internal organs (brains, eyes, and even cilia). The player can also pick weapons and powerups. Powerups include speed boosters, increased firepower, homing missiles, and shields similar to the "Option" featured in Gradius. For weapons, the player starts with the normal pea shooter, but can upgrade to a 3-way gun, a spread fire gun, a laser, and a hoop-like weapon. However, like most shooters, if the player is killed, all of the upgrades will be lost and the player will have to restart from the last checkpoint. In some cases, if the player dies, they may have to navigate through enemy fire with slow speed, which could prove more difficult than ever.
Another aspect of Abadox that sets the game off from other shooters is the second, fourth, and sixth stages. The play style changes from a side-scrolling perspective to a vertical one, but instead of scrolling upwards like a typical vertical shooter, the stage scrolls downward. The final stage involves an escape sequence where the player must navigate out of the alien's rectal cavity before the alien implodes. This falls in suit with another Konami game, Life Force, which Abadox bears a striking resemblance to.
Source: Wikipedia, "Abadox", available under the CC-BY-SA License.