Det enorma grottsystemet, känt som Abyss, är den enda outforskade platsen i världen. Ingen vet hur djupt ner går denna Titanic grop, bebodd av konstiga och underbara varelser och full av mystiska forntida reliker som syfte i okända för den moderna människan. Generationer av djärva äventyrare har dragits av kryptiska djup avgrund. Under tiden de djärva nog att utforska den farliga gropen kom att kallas "Cave Raiders." I Orth, staden vid kanten av avgrunden, bor ett litet föräldralöst namn Rico, som drömmer om att bli så stor en grotta Raider som hennes mor var och lösa den stora mysterium gropen. En dag att utforska den dunkla djup hon snubblar på en liten pojke, som visar sig vara en robot.

It is many thousand years in the future. Vampires once ruled the night but have seen their numbers reduced by fearless bounty hunters. One such hunter is D, the halfbreed son of a human mother and vampire father. When a girl from a rich family is taken from her home by the vampire Meier Link, her father contracts both D and the Markus brothers (a rival group of hunters) to race to retrieve her. As the heroes fight their way through Meier's hired guards, they begin to suspect that the girl may have gone with him willingly.

The year is 2016. The place is New Port City. The Tank Police are still waging a desperate war on crime, and their tactics are still highly questionable. Mayor Weatherby is trying to pass a bill banning certain weapons from the city, which makes her a target of the Dai Nippon Geiken Corporation, who are now manufacturing mobile weapons that even the Tank Police may not be able to stop. Dai Nippon Geiken is also connected with the murder of Leona Ozaki's former partner, Charon Ishira, making the battle all the more personal for the Tank Police's number one officer, who will stop at nothing to avenge her partner. But can she pay the high price revenge calls for?

A young boy stumbles into a mysterious girl who floats down from the sky. The girl, Sheeta, was chased by pirates, army and government secret agents. In saving her life, they begin a high flying adventure that goes through all sorts of flying machines, eventually searching for Sheeta's identity in a floating castle of a lost civilization.