The year is 2028. A giant alien ship called the "Hivecraft" appears in Earth, flying across all major continents in the span of three days, dropping monstrous, insect-like creatures and deadly, highly-advanced weaponry in its wake. Major population centers are abandoned and reduced to ruins in a manner of months; major military bases worldwide are destroyed; and though a new military organization (dubbed the "Earth Defense Force" is created in response, it ultimately seems that nothing can be done, and humanity waits and watches the end of history unfold before their eyes.
2032. A groundbreaking technology is created, the "PA-Gear." Exo-suits deriving power from the mysterious minerals that are inside the aliens and their technology, they finally give humanity the edge they need to push back against the aggressors, slowly taking back their planet with teams of small, but devastating forces of EDF soldiers. The alien's expansion is stopped, humanity reforms society around this new paradigm.
2033. With the help of a brand new, still-experimental "Type-S" power core and PA-Gears for their ace soldiers, the EDF stages an all-out assault at the Hivecraft. Their overwhelming numbers and skills completely demolish the Hivecraft, but the victory is not without its costs: half of the already tiny EDF forces are killed, and the experimental cores end up completely lost. Worst still, the insect-like monsters it dropped remain.
2040. Without the guidance of the Hivecraft, the giant insects breed uncontrollably, turning the ruins of cities into their massive hive complexes. Outnumbered and exhausted, EDF falls, and only surviving patches of assorted military units survive. In the remnants of central headquarters, they plan, prepare, and strike out in the insect-infested wastes, trying to help humanity survive another day in a world ruled by giant insects.
Such is the plot of Earth Defense Force: Iron Rain, another spinoff to the Earth Defense Force series. The core gameplay of "shoot giant bugs with various, increasingly ridiculous weapons" is the same but there are numerous changes to the mechanics. By far the most obvious is that the class system has been replaced, all weapons able to be used by all characters, with PA-Gears deciding mobility options and special abilities. Among the base four:
- Trooper: The classic all-rounder, capable of sprinting and rolling across the battlefield, using their vast repertoire of supplies, gadgets, and vehicles to answer any and all situations that may arise.
- Jet Lifter: The most mobile and agile of the four, they can take to the skies and rain down hell from high up above, though their durability leaves much to be desired.
- Heavy Striker: Effectively a tank with legs, they are the most durable, having immense amounts of armour, health, and a shield which nullifies incoming damage, and the most destructive, capable of dual-wielding any weapon in the game and increasing their firepower exponentially.
- Prowl Rider: The latest in PA-Gear technology, they use their revolutionary "E-Needle" to hook onto and zip across the battlefield, or use it to control domesticated giant insects known as "G-L.I.A.R." (Ganglion-Linked Intelligent Aggressor Reinforcement)
Other changes include an "Overdrive" mode, a once-per-mission power-up that grants them unlimited energy, vastly increased firepower, or becoming effectively invincible, among other benefits. The weapon acquisition/upgrade system has also been vastly streamlined, now requiring investment of resources and currency rather than finding them as random drops.
This game provides examples of:
- After the End: It's been 12 years since the aliens arrived and completely destroyed the earth. Most of the game is largely spent trying to improve your odds of survival, than drive the aliens out and retake the world.
- Awesome, but Impractical: Loading up with the most ridiculously overpowered and high-ranking items/deployments/vehicles as a Trooper. Sure, it will be great fun to ride one or two heavily-armed tanks, running over and tearing the giant insects several new ones, all while your fancy turrets take care of anything that somehow manages to survive, but unless you've got ridiculous amounts of resources stockpiled, you'll only get to use it for the one or two missions before you're broke.
- BFG: A good number of weapons, ranging from portable artillery, miniguns, to laser cannons. Unlike previous entries in the series, everyone can use them.
- Boring, but Practical: Though Troopers are not restricted from using any of your increasingly ridiculous arsenal, they have no special abilities except having more item slots and carrying capacity. While you could theoretically load-up with swarm-shredding auto-turrets and badass vehicles, the costs of deploying them oftentimes means you'll be running with cheap, dependable, but mundane items like mines.
- Character Customization: A first for the series. Whereas previous titles limited you to the two-tone colour-scheme of your standard armour and a single, gender-locked model for each class, here you can deck out your soldier with all manner of variant models, or simply have them running around the field in their underwear with their exo-suit as their only sensible protection.
- Cycle of Hurting: An issue with the game is there is a lot more knockback than main EDF games in addition to knockback giving you no invincibility. Even normal ants can knock you over with their acid. This can leads to problems where you get swarmed and continually take damage while helpless unless you Overdrive or manage to move out of the crowd fast enough.
- Darker and Edgier: While the previous EDF titles have always (attempted) to delve into serious, dark drama with the implications of a massive, extinction-threatening alien invasion, missions tend to take place in bright, colourful, and thriving population centers, most of the carnage happening off-screen and by way of radio reports. Here, though, you can definitely see that the empty, abandoned, ruined wastelands the aliens have turned earth into, and the player characters operate out of the abandoned remnants of what used to be EDF central headquarters.
- Disaster Scavengers: While the EDF and the Kindred Rebellion are both technically this, it's much more prominent with the latter who spend most of their appearances stealing the power gems from the giant insects you've killed. It should also be noted that the Prowl Rider PA-gears were formerly Kindred technology, until the EDF scavenged and reverse-engineered it.
- Double Unlock: Unlike the main games, where you got random weapons that were ready to use as soon as you got them, here you unlock predetermined new weapons based on the level and difficulty of the level you complete and must buy them with credits and energy gems after unlocking them to use them.
- Early Game Hell: A big issue with the game is the weapons you can get starting off the game can best be described as "pea-shooters" or "gimmicky weapons with too many drawbacks", with only a scant few early game weapons being powerful and useful enough to be helpful, while the game introduces tanky enemies and throws out swarms quite readily. Once you get a bit further into the game you'll finally start getting gimmick weapons that are worth the drawbacks that will help you out getting through levels before you start getting a respectable arsenal open to you.
- Earn Your Happy Ending: Despite the impossible odds, no shortage of casualties and moments of despair, the EDF wins against the Aggressors once more, sending the main forces into retreat, deactivating the automated ravagers, and forcing the giant insects into extinction.
- Elite Army: Compared to previous games, EDF now deploys small, highly-trained, and well-equipped squads that can do far more than hordes of largely-disposable troops. In the campaign, the PC "Closer" belongs to the Blast Unit.
- Enemy Mine: Eventually, the EDF and the Kindred Rebellion agree that putting their limited resources and manpower together against the aliens is a much better use, than constantly robbing and assaulting the other.
- Fragile Speedster: Jet Lifters are fast, agile, and are capable of using some serious firepower, but have the poorest armour ratings of all the PA-Gears.
- Green Rocks: The Energy Gems that fuel the giant insects, and all of the surviving technology, PA-Gears in particular.
- Guns Akimbo: One of the Heavy Striker's biggest appeals. The accuracy they still have while firing two mininguns at once can be easily explained by the fact that its their powered exo-skeletons doing most of the lifting and recoil compensation for them.
- Mêlée à Trois: When the Kindred Rebellion shows up on the field, they will attack the EDF, but still fight the giant insects, who will try to eat the both of you.
- Mighty Glacier: Without their limited boost, Heavy Strikers move very, very slowly. However, with the ability to carry up to four separate pieces of heavy ordnance, using two at any given time, you really only need to get within range.
- No Plans, No Prototype, No Backup: Justified. The lore specifically states the experimental cores of 2033 were still being studied when they were deployed in real combat, and logistics and supplies were already difficult with the on-going collapse of society, what more during the catastrophic aftermath of the Hivecraft's destruction?
- Powered Armor: All the classes, with the Heavy Strikers having the most bulky and obvious gear of all of them.
- Power-Up Mount: The Prowl Rider's ultimate ability is to activate their "G-L.I.A.R." system, summoning forth a domesticated giant insect to ride as a beast of battle.
- Super Mode: "Overdrive," the defining feature of the "Type-S" core and PA-Gear that the PC "Closer" has exclusive use of. Activating it gives them vastly increased firepower and reload speed, unlimited energy, and regenerating health, along side other perks depending on the PA-Gear.
- Super Prototype: The experimental cores of 2033 for the "Type-S" PA-Gears were key to the destruction of the Hivecraft, lost to history until Closer (the player character) was rediscovered and pulled out of their coma.
- Walking Tank: The Bigfoot vehicles. In a nod to the severe impracticality of this design in real-life, the lore mentions that the first generation was so slow, clumsy, and effectively helpless without infantry support, they actually spurred the creation of the PA-Gear. The newer generations seen in-game, especially the Marauder, have largely solved these issues.