In the future, humans have colonized Mars for three centuries and are near completion of its terra-formation. Other than political friction with Earth, it is considered humanity's Golden Age. One day, contact with the Vesta asteroid mine was lost. The asteroid had been taken over by a hostile alien force that would be become known as "First Approach" (F.A). The F.A began causing terrible destruction and then suddenly vanish before anything can be done to stop them. In order to combat this threat, the Solar system Defense Force (SDF) was established. However, irregular electromagnetic waves from The Seed, F.A's power source, will cause the SDF's unmanned fighters to malfunction. In response, the SDF adapted the Remote Artificial Intelligence Network to allow remote control of their newly developed space fighter, Antares.
The first three levels are virtual combat simulations to let Frank Boyd, the pilot, get acclimated to using the RAIN system to pilot three Antares fighters at the same time. Frank's training is interrupted by an F.A, codenamed "Isis," hijacking the battleship Osiris inside a colony. This turns out to be a diversion to allow the F.A time to take over the Ziggurat Space Elevator, topple it, and destroy the Martian capital of Sheffield. Frank assumes control of three fighters left at the city and disables the core of the elevator. Then, things get worse.
This game is known for the "Border System" and its unique scoring method.
Tropes used in Border Down:
- Always Close: The boss scoring method. Unlike other Time-Limit Boss scenarios where you are awarded more time the more your remaining time is, in Border Down, you're awarded more points the closer to 0 your remaining time is.
- Battle in the Rain: 6-D has the final battle take place in stormy weather, contrast to 6-C, which had the stage take place in sunset.
- Beam-O-War: When an enemy fires a laser similar to your Break Laser, a large ball of energy is created that takes up a large portion of the screen. Small enemies and enemy shots are destroyed. Large enemies and bosses will take more damage compared to the Break Laser alone, but only if the energy ball is touching them.
- Continuing Is Painful: The Border System. When you start the game, you are given a choice of three difficulties/paths: Border Green for easy, Border Yellow for medium, and Border Red for hard. Choosing a harder difficulty allows for a higher score, but you technically only have one life on each Border. If you're on Green and you die, you Border Down to Border Yellow. If you die on Border Yellow, you Border Down to Border Red. And if you die on Border Red, it's Game Over.
- Inverted with actual continues because you keep your score, keep your progress on the Stage Norm meter, and you start at Border Green regardless of what Border you started the game with.
- Deadly Walls: Sort of. You can rub against a wall for a little bit, but continuous rubbing will kill you.
- Do Well, but Not Perfect: Which version of stage 6 you get is determined by which Border you've spent most of your time in. 6-A is if you don't have a dominant border (meaning you've probably been choosing at random), 6-B if Green, 6-C if Yellow, 6-D if Red. 6-D might sound like the best idea, given you have to prove yourself in the toughest Borders, but that actually gets you a worse ending than 6-C. In effect, you have to avoid taking the easy path (lest you get stuck in the simulacrum), but also want to give yourself some wiggle room. It may also reflect the idea that in-story, "Red Border" usually means "got clocked in the Yellow Border" — you didn't do perfectly after all.
- Downer Ending: The only difference between the 6-D ending and the level 6 Nonstandard Game Over is Frank's brain got fried by the RAIN system and left in a vegetative state. 6-C is a little more hopeful; Frank's at least somewhat back in a properly conscious state, although the immediate terraforming is emphatically not going to work out. Also, it seems Frank's willing to give RAIN another go. Considering that he successfully wiped out the Earth conspirators' own version of Antares, and he has a better grip of what RAIN does... the question is whether the conspirators can still control RAIN's output.
- Earn Your Bad Ending: 6-D. See Do Well, but Not Perfect and Downer Ending above for more information.
- Engrish: The Engrish is good enough to let English-speaking players know what the story is, more or less.
- Every 10,000 Points: The Stage Norm quota. Reaching it allows you to go up one border at the start of the next level.
- Government Conspiracy: The First Approach were actually a fiction of the Earth officials behind the creation of SDF. SDF and RAIN were all just a ploy to (a) rip up Mars and force it back under Earth's rule...with Frank himself as a convenient fall guy for the disaster... and (b) design the ultimate battle machine — Red Wasps, the heavily armored versions of the Antares fighters that act as the 6-C and 6-D bosses. Even worse, everything but 6-C/D was a simulacrum fed to Frank to force him to ruin the space elevator...
- Hallucinations: The bosses for level 3 & second half of the level 5 boss. All of level 6, depending on how many Stage Norm clears you got and how much time is spent playing in the three Borders.
- Hitbox Dissonance: Shots can pass through your ship and won't blow it up as long as it doesn't touch the hitbox in the center. However, it will blow up if the ship itself, not the hitbox, crashes into solid objects.
- Mirror Boss: The Final Boss in Stage 6-C/D.
- Nice Job Breaking It, Hero!: In level 5, the mission is to disable the elevator core just enough to prevent the SEED from activating, but not to the point that it will explode. This is accomplished after the fifth boss's first two phases. Unfortunately, phase three is Frank hallucinating that it isn't defeated after all...
- Nintendo Hard: The game itself is hard. It seems impossible at first because you can only play sections of a level in Practice Mode that you've reached in Arcade or Remix mode, continues unlock over time, and you don't start with any. Worse, the Border system means that the game gets harder the more you die.
- No Ending: Fail to defeat the Final Boss in either version of Stage 6 within the time limit, you get no ending at all.
- Nonstandard Game Over: Level 1, 2, & 3 show excerpts from the SDF's reports about the RAIN system.
Level 4 shows Frank visibly distraught after failing to stop the Osiris and being consoled by his CO.
Level 5 shows the wreckage of the Antares and some of the space elevator in orbit after it fell onto the Martian surface.
Level 6 shows the massive canyon caused by the space elevator falling to the ground. The terra-formation of Mars is set back 100 years, the Martian economy collapsed, the Martian government fell into disarray, and Earth had to send its military to Mars to establish a provisional government.
- Press Start to Game Over: If you start the game on Border Red, it is possible to end the game near-immediately by taking a hit by one of the first enemies. Considering that the game is very Nintendo Hard on Red, this is very, very much possible.
- Space Elevator: F.A. tries to topple one on Mars to destroy the capital city. Frank tries to stop them, but hallucinations cause him to destroy the elevator by mistake.
- Spiritual Successor: Successor to Metal Black. Hiroyuki Maruyama, the president of G.rev, started the company and did subcontracting work for Treasure and Taito to generate revenue just to make this game. Why? He just really liked Metal Black.
- Time-Limit Boss: Subverted; the timer is used to calculate the bonus points you receive when you defeat the boss, with higher bonuses the closer the clock is to 0:00 remaining. If you fail to defeat the boss before the timer reaches -30 seconds, you still proceed to the next level, but take a hefty 6 million points in penalty.
- Let it hit -30 in Level 6, and it's game over, playing the trope straight.
- Title Drop: When your ship is destroyed and you see whether or not you got close enough to the checkpoint to start the next border at the second half of the level or the boss fight.
- True Final Boss: Only accessible in 6-C/6-D, where you must fight duplicates of your fighter.
- Unstable Equilibrium: Score high and avoid dying and you'll be allowed to stay on the Green and Yellow borders, where the score quota to be able to go up a Border is lower. Play poorly and die, and you'll get stuck on the hardest border, Red, where enemies are fiercer, you need an exceptionally high amount of points to go up one Border, and the next hit means a Game Over.
- With Great Power Comes Great Insanity: The RAIN system. The fact that piloting three space fighters with three separate missions via a remote control neural link overloading Frank's brain might have something to do with it. Except for the battles in 6-C and 6-D, everything Frank experienced — hallucinatory experiences included — was custom-made by the Earth conspirators to manipulate him into doing their dirty work for them... They WANTED him to break. That way, he could easily be disposed of, and/or unable to mount a proper defense against being blamed for the space elevator disaster. But if 6-C is anything to go by...