What's true main story of "Yu-Gi-Oh" series before it was about TCG?
In the initial stages of the manga, Yu-Gi-Oh was more or less supposed to be a horror manga. Although the end result was a manga about games, it was clear that some horror elements influenced certain aspects of the story. It was later decided that "battle" be the primary theme. Since there were a lot of "Fighting/Combat" based manga, it was in a way difficult to come up with something original. Hence it was decided to create a fighting based manga where the main character does not hit anybody.

Hence, the early chapters of Yu-Gi-Oh feature a variety of different games; but from chapter 60 (volume 7) onwards, the most common game that appeared as a plot device was the Duel Monsters card game (formerly known as Magic & Wizards) through the Duelist Kingdom and Battle City tournament arcs; receiving elevated plot relevance in the latter arc. 

Other games still appear during the DDD and Memory World portions of the manga and gaming, in general, is often referred to; the modern card game being a recent fad in Japan imported from the United States within the original story.

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