Wikia

In Roman history, the names Caius and Gaius are interchangeable. This card's name can therefore be a reference to many powerful figures of the late Roman Republic, including Gaius Gracchus, Gaius Julius Caesar, and Gaius Augustus.

This card appears to be conjuring a "Dark Core", whose effect is similar to this card.

As referenced in the artwork of "By Order of the Emperor" and "March of the Monarchs", "Caius" may be a leader over all the other Monarchs. As further evidence of this, Caius's effect is arguably the strongest, being able to target any card on the field , while most other Monarchs have restrictions on what their effects can target, and they only destroy their targets while Caius banishes his. Also, as mentioned above, Caius shares his name with Gaius Julius Caesar and his son, Augustus, the two first and arguably most famous Roman Emperors.

This card along with "Dimensional Alchemist" were the only TCG Structure Deck cards that were reprinted as Gold Ultra Rare. As it happens, these cards both were first printed in the same Structure Deck being The Dark Emperor.

Also, the background of Caius' artwork appears to be Dark World, implying that Caius is also the ruler of that dimension.
- There is also the possibility that Caius is attacking the Dark World. This is supported by the Dark World resulting in discarding to the grave, while Caius removes from play, something that could heavily hinder a Dark World deck. The same goes for "Dark Core". The card, "March of the Monarchs" could depict Caius leading the other Monarchs on the attack of Dark World.

Card Trivia:Caius the Shadow Monarch