One day, a mysterious army of deadly robots called the "Ajiths" suddenly appeared out of nowhere. Where they came from is unknown, but no matter their origin, the world was quickly decimated. Anyone who managed to survive the war found themselves desperately hiding in the ruins of human civilization or taken into slavery by their new robot overlords. Three years after the takeover, Reika Rekkeiji is in the latter position, awaiting her fate in a jail cell following the deaths of her friends and family... at least until a mysterious girl breaks into her cell to rescue her. The jailers quickly learn of the break-in though, so this girl goes with Plan B: pull a gun on Reika and tell our heroine that she's a kind person, but must die for the sake of humanity. Before Reika can even figure out where this girl came from, much less how she knows her name and what she's even talking about, the girl manages to shoot her arm clean off before being dragged off by some Ajith soldiers.
Fading in and out consciousness from blood loss, Reika gets a second visitor: the Mad Scientist Dr. Kouzuki, who promises to help her survive if she becomes his guinea pig. With her only other option being to bleed to death on a pile of rubble, she agrees, undergoing an operation to become a cyborg with ferrokinesis and the ability to manipulate nanomachines. With her new skills, and with the help of Dr. Kouzuki, humanity may now have what's needed to finally fight back and reclaim Earth.
Giga Wrecker contains examples of:
- Amazon Brigade: It's implied that all (or the majority of) the Ajiths are female, based on the fact that all of the game's bosses are female.
- And Your Reward Is Clothes: Basically, any weapon data aside from the one demanded by the plot is this. The skins are thematical: pixel, fish, sweets, legends and Astra (mimic the bosses of the weapons' respective areas).
- Aw, Look! They Really Do Love Each Other: Take out Vinata first during the 2nd go around and Kadrū is this, commenting sadly and angrily that Vinatā won't be around to annoy her anymore. Then it gets a bit subverted one second later as Kadrū starts gleefully thinking about what to do with Vinatā's scrap parts.
- BFS: Astra Vinatā's sword. If you actually bother to search for hidden content, you can use it too.
- Bunny-Ears Lawyer: Shiori Shiragami. While she acts weird, she can communicate with you even when Dr. Kouzuki can't. Or so she tells you.
- Conveniently Unverifiable Cover Story: "Shiori" introduces herself as Dr. Kouzuki assistant. Since you can't communicate with him, you have no way of knowing.
- Evil All Along: Shiori. Also known as Astra Kadrū.
- Five-Second Foreshadowing: Astra Saramā uses some kind of Time Stands Still attack. Right after her boss fight, you get the Tachyon Handler.
- Foreshadowing: "If only there were a way to get it back to how it was before it collapsed..." Yeah, really subtle, Reika.
- Future Me Scares Me: It is implied that the Big Bad is actually an older Reika. The original game merely heavily implied it and no one seems to ever realize the truth, even the Big Bad as she's dying, but everyone discovers the truth in Giga Wrecker Alt's version of the ending scenes..
- Level Editor: You can make levels in an editor. Levels made by others can played from the Custom Campaign menu and be found on Steam Workshop.
- Mad Scientist: Both Dr. Kouzuki and Astra Kadrū. They end up getting along rather well because of that.
- Mysterious Waif: The girl from the intro, a.k.a. Amane Azuma.
- Save Point: Blue orbs act as save points by recording memories as particle data. Reika gets confused when she reads a sign next to one.
- Spared by the Adaptation: Maybe. In the original version, the Big Bad Mahāstra Tārā can do nothing but scream and beg for someone to tell her where she went wrong before closing her eyes as her fortress falls apart around her and everything fades to black. Giga Wrecker Alt adds an epilogue where Dölma finds her (or what's left of her) in the wreckage and still alive. Reminiscing on how she created Dolma to preserve her good emotions allows her to finally regain some of her humanity back. Although it's not entirely certain that she survives beyond that because at this point her entire body's been torn apart besides her upper torso and head and she's leaking fluids all over the place, but she seems to be in good spirits at least.
- Token Evil Teammate: Astra Kadrū, an evil scientist who doesn't care about ethics when it comes to For Science!, and she also relishes in causing despair and misery. She's also a Bad Boss who believes We Have Reserves, not willing to upgrade Ajith defenses because shock absorbers are expensive.
- Token Good Teammate: Astra Vinatā, who believes in honor and justice. And a Benevolent Boss as she's constantly bugging Astra Kadrū to improve Ajith survivability. Needless to say, the two don't get along.
- Was Once a Man: Some of the Ajiths. You can later find logs for all of the bosses you've encountered, except for Astra Saramā, and you don't need a log to know who she used to be.