The Black Spots, giant black spheres
that simultaneously appeared around the world, engulfing large parts of many major cities. From them, armies of monsters appeared and attacked indiscriminately. These monsters were called Zillions of Enemy X, or ZX (pronounced "zecks") for short. For a time, mankind had no means of fighting back. However, after the development of a special device that allowed people to contract and control certain ZX—a technology promptly entrusted to the military and law enforcement—many urban areas were able to regain stability.
However, all is not as it seems, as the armies that lay in wait on the other sides of the Black Spots are waiting. They enlisted humans to fight for dominance, and are determined to conquer one another, with little regard for the humans caught in the middle of their war.
Enter Asuka Tennouji, an ordinary young man who's lucky enough to live in an area of Japan that's regained stability despite being in close proximity to a Black Spot. On his way to his part time job (on Christmas Eve no less), an impromptu shortcut leads to a chance encounter with a strange girl dressed as a priestess. She claims to be the priestess of the dragons, and entrusts Asuka with a device that allows him to catch and control ZX, and tells him to protect the world. Later on that very same day, Asuka has a chance encounter with a powerful angelic ZX...
This work contains examples of:
- The Ace: Fierté apparently has power to rival one of the Twelve Apostles, but due to the whole In Medias Res thing, we don't find out what this means.
- Added Alliterative Appeal: Most of the humans' name with A.
- Ax-Crazy: Gambiel. Kills a group of angels just because they saw Fierte and were going to tell Michael about it, orders an entire human village slaughtered just because an angel accidentally killed a human, finds the destruction caused by Audium to be "fun", many of her expressions during the series make her seem rather... unhinged, and her reaction to getting her cheek cut by Sieger was to try to kill everyone present while continuing to smile like a madman...
- Big Eater: Azumi is shown to be one in episode 3, much to Asuka's surprise.
- Blackmail: This is basically what the Blue World figures did to Azumi. Offering her a cure for her condition if she became a killer for them.
- Blood Knight: Sieger loves to get his claws bloody, and he's very proud of it. Alexander is the same way whenever he finds prey he considers worthy, not caring about the damage he causes during the battle.
- Collectible Card Game: Called simply "Z/X", it isn't portrayed in the show other than featuring "card devices" that the Z/X reside in.
- Expy: Alexander comes from a world where the greatest among his Braver class are called the 9 Heroes, and he is King. He has a gold and orange color motif and when he defeats an enemy with his most powerful attack, an Air Drill that he forms when he brings his hands together, he shouts Return to Dust. Finally he is voiced by Nobuyuki Hiyama. If this is not an expy of Guy Shishioh from King of Braves GaoGaiGar then nothing else can be.
- Fluffy Tamer: Sera is a small 7-8-year-old girl with a twenty-foot-long brass Tyrannosaurs Rex for a companion.
- Freudian Excuse: Ayase and Sieger has been murdering Angelic ZX's, and it's revealed the angels killed her parents.
- Genderblender Name: Michael, one of the four archangels, is female.
- Gentle Giant: Orichalcum Tyranno, though only to Sera.
- Gorn: This series can get very bloody.
- Ill Girl: Azumi is sick with an illness that human science can't even identify, and stays alive only thanks to the medicine provided by the Blue World's Administrators. Azumi has been infected with nanomachines and the medicine she has been taking regulates the amount of poison they produce. Rigel was not happy to discover this.
- In Medias Res / How We Got Here: Most of the first episode takes place on New Years Eve and drops you right into the middle of the action, with minimal exposition and Arc Words in abundance, leaving the viewer to fill in the blanks. The last third of the episode skips back to Christmas Eve and Asuka's becoming a ZX Fighter. Episodes 2 to 6 then build back up to the New Years' battle, and episode 7 shows the events of the first episode from a different perspective.
- Insistent Terminology: Because Alexander refuses to retreat Mikado insists that they are not retreating, they are just heading to a supply base to resupply and rpepare for future invasions.
- Kansai Regional Accent: Asuka, justified since it takes place in Kobe, a city in Kansai.
- Large and in Charge: Gabriel. His first appearance is less of an appearance and more of a background shift.
- Last Episode New Character: Asuka's brother Yamato briefly appears in the last episode.
- Leave No Witnesses: Gambiel orders an entire village slaughtered just because some angel accidentally killed someone.
- Nice Guy: One of Asuka's defining characteristics.
- Oblivious to Love: Asuka. He seems to have no clue that Ayase has fallen in love with him, and his reaction to Aina flat out confessing her feeling for her was to say that he loves her too... because they are friends.
Aina: I like you, Tennoji!
Asuka: I like you too, Aina! We're friends, after all!
- Panthera Awesome: Sieger, who is a panther.
- Screw the Rules, I'm Doing What's Right; Why Garmatha betrayed the angels and saved Ayase when Gambiel had them slaughter an entire village of humans to cover up one accidental death.
- Sequel Hook: The second half of the anime's last episode is full of these. Some of the more important ones:
- Michael calls Ayase "Ayase-oneesan", and Ayase calls Michael by the name "Sakura". The two clearly know each other, but nothing more is revealed about their relationship.
- Polaris, one of the Blue World's Administrators, and the Shrine Maiden that gave Asuka the Card Device have a cryptic conversation about the future of all the worlds.
- Gambiel returns to the White World and has a conversation with Gabriel that implies he has plans of his own, and said plans seem to involve Audium's broken mask that Gambiel brought with her.
- Viewers Are Goldfish: The shows feels the need to paste the characters names, locations, and even the time on screen every five minutes.
- Winged Humanoid: Fierté and most of the White World Z/X.