The X-Antibody (Ｘ抗体 X-Kōtai?) is a plot element from Digital Monster X-Evolution, Digimon Chronicle, Digimon D-Cyber, and the related virtual pets and card games. It is a vaccine that makes Digimon immune to the X-Program, and most Digimon that are introduced to it also become more powerful than their normal counterparts; they are differentiated from their original forms by the suffix "X" or "X-Antibody". There are also many species of Digimon who are natural carriers of the X-Antibody, and do not have a separate "original form".
When the Digital World became so overpopulated, the super computer that governs the Digital World, Yggdrasill, wasn't able to handle it anymore. His solution was to wipe out the vast majority of the Digimon with the X-Program, and choose a very small percentage to be moved to a new Digital World, and destroy the old one. Those who were not chosen but still survived and moved to the new world had a rare gift known as the X-Antibody. This antibody, when activated, changed their appearance and strength.
Those who have the X-Antibody are generally distinguished by the X in their name and sometimes an X placed on their body somewhere or a gem (example: Dorumon's on his forehead, WarGreymon X's on the front portion of his front horn). There are few with the X-Antibody that isn't distinguished by an X after their name because there is no other version of them in existence.
The X Digimon fled to a new Digital World which was split into three Terminals (the three terminals are named after the Norns from Norse Mythology) consisting of Urd, a past plain which is a volcanic wasteland, inhabited by dinosaur and dragon Digimon, Verdandi is the present which is a world of lush greenery and is home to beast, bird, plant and other nature Digimon, and Skuld is the future, a high-tech city where machine and insect Digimon dwell. Yggdrasill sent the Royal Knights to eliminate the X Digimon.
While X Digimon appear in Digimon D-Cyber, Yggdrasill and the X-Antibody are never mentioned, as all Digimon are already X Digimon. Furthermore, while the Royal Knights who appear in X-Evolution and Chronicle are main characters, they are never shown to have any kind of mission to exterminate the X Digimon.
Also, in America, Digimon with the X-Antibody are prominently featured in the card series Digimon: Operation X Certain Digimon have the X Antibody, some Digimon are vulnerable to these Digimon, and another group of Digimon can easily destroy Digimon with the X-Antibody. Modify cards can also add, destroy, alter, or get power from the X Antibody.
The X-Program (Ｘプログラム X-Puroguramu?) is a termination program initiated by Yggdrasill in the 8th Digimon movie Digital Monster X-Evolution to eliminate 98% of Digimon as a result of the exponential growth of Digimon causing the Digital World to reach maximum capacity. When the X-Program was executed by Yggdrasill, 98% of the total Digimon population was eliminated. The remaining 2% were transferred to the NEW Digital World where the X-Program could not reach them. However, a minority number of Digimon strong enough to resist the effects of the X-Program were able to survive by changing their DigiCores. The Digimon were reborn in a form that could take in the X-Program and eventually it came to a point where a program that opposed the X-Program was installed into the DigiCore—the X-Antibody.
The X-Antibody Indicator (Ｘ抗体インジケーター X-Kōtai Indikētā?), also referred to as the XAI System (ＸＡＩシステム Sai Shisutemu?) is a system which displays the status of the X-Antibodies. If the XAI system is activated, via the Pendulum X, and it detects the X-Antibody present, it will begin to alter the Digimon itself, resulting in an X-Antibody Digimon.
List of X-Antibody carriers
- Natural carriers
- Other carriers