User:Kousaka/A Certain Scientific Card Game

This page details the ideas behind a hypothetical A Certain Magical Index and Yu-Gi-Oh! crossover.

= Concepts =

Science Side
The Science Side of Index is Academy City, a city of progress and technology that is home to the Espers. Espers are individuals whose brains have been hard-wired to perceive reality differently. Through this rewiring, they can enforce this "Personal Reality" of theirs onto the real world, performing complex mathematical calculations on their surroundings to manipulate the environment, which manifests itself in a superhuman power.

Espers' powers
In the crossover, Espers' Personal Realities cause the subconscious creation of unique card data that is stored in a Duel Disk with Solid Vision generating capabilities (similar to Arc-V's disks). They use these cards as a reference point for their calculations and conduct battles with Duels. Espers are also the origination of Synchro and Xyz Summons, the Summoning methods said to be derived by science. In this universe, the ability to summon these monsters requires a manipulated Personal Reality to manifest in the at all. Thus, ordinary individuals and Magicians cannot perform Synchro or Xyz Summons at all, barring the use of Esper-simulating technology by researchers.

Espers also have inherent effects tied to themselves, which can be activated anytime, as long as the requirements are met. Most of the effects greatly boost consistency and synergize with the Deck they themselves generate, allowing all of them to access their power plays much earlier than an average Duelist. In this way, Espers are like physical extensions of their Decks, having effects themselves to use as if they were a card in their own Deck. However, the Esper power curriculum has fundamentally changed their minds and bodies to such an extent that they can't use the Summoning methods derived from magic, Ritual and Fusion Summoning, without incurring serious harm to their bodies.

Levels
Espers are tiered by their power level into six level categories between 0 and 5. These levels scale exponentially; the gap between a Level 0 and a Level 1 is very large, but the gap between a Level 1 and a Level 2 is even larger than that, as is the gap between a Level 2 and 3, and so on. In the crossover, each increase in Level grants an Esper access to a new activated effect for Dueling, with Level 5s having five such effects at their disposal. Barring extreme extenuating circumstances (or the presence of ), a lower-leveled Esper will never defeat a higher-leveled Esper in combat.

While the researchers of Academy City purport that anyone can rise through the Levels with enough study and hard work, the truth is that said researchers are the ones in control of everyone's development. Those who are seen as "worth the investment" to raise in Level are given sufficient support to develop their powers, while those who are predicted to take longer to unlock their potential are discarded early on or never even given a chance in the first place.

The 7 Level 5s of Academy City

 * See also: Decklists: A Certain Scientific Card Game/Science Side

Academy City's Level 5s are the strongest Espers in existence, with borderline reality-bending potential in their powers. The Decks they generate are completely and utterly broken, as are their Esper abilities, and they rarely, if at all, lose in a straight-up fight, except to each other.

Numbers
In the Duel Monsters AU of A Certain Magical Index, Numbers are special Xyz Monsters generated through unexpected distortions caused by espers' AIM Diffusion Fields.

Espers unconsciously create cards through their AIM fields. However, most of the monsters that they create stay within a certain, predictable Summoning energy range given their Level and projected capabilities. "Number" cards, on the other hand, have a Summoning energy that greatly exceeds their other monsters'. It is not entirely understood why espers sometimes create these cards, and why they all fall under the same archetype of "Numbers"; to this end, the "Numbers" are heavily researched by Academy City's elite, with a few unscrupulous individuals even seeking to use this data in hopes of replicating this power for themselves.

Higher-leveled Espers tend to have a greater chance of creating "Numbers." Those who fall into the trap of using the Level Upper may find themselves in possession of a "Number" due to the massive changes that the program causes to their brain functions, which disappears after the effects of the Level Upper wear off. Those "Numbers" do represent their original owner, but do not necessarily become exclusive to that person. If they can increase their Esper level organically, they may be able to regain that "Number"; otherwise, it may manifest itself in another fitting esper's Deck.

Original

 * Note: A "↑" indicates that the original owner's level had been artificially increased by the Level Upper while the "Number" was in use.

Over-Hundred Numbers
= Duel History = In the crossover, there are two main categories of Duels:
 * A Master Duel is the lowest-stakes Duel available. It follows the rules of the real card game; neither player can activate their Esper abilities, and other Duelists cannot intrude onto the game.
 * An Open Duel is a low-stakes Dueling environment that incorporates the use of Esper abilities, but not Duelist intrusions. It may be played as a Battle Royale.
 * An Unrestricted Duel is a real battle, and the most common Duel played in Academy City. In an Unrestricted Duel, Life Points are tied to the player's actual physical vitality, where taking damage puts players in real danger. Other Duelists can intrude onto the fight at any time, with an intrusion penalty in place. Additionally, nearby structures and environments (represented as cards) can affect players' fields and Esper abilities alike.

Duels marked with (*) do not occur in the original canon.