Why was Kit's Deck the only one without a Contract?
 

All the deck's that Xaviax's has given out come with the contract beast intact. Kits' deck was blank and he had to merge with the Dragon to get his full form. We have seen Rider's vented and their decks remain intact. So it is interesting to wonder why exactly Kit's deck was different. Could it tie into something that happened to Adam? Who was aparently Vented at some point. Unless there is a plot twist there.

I can tell you why, source footage.

I have a theory
 

Here what I think: after Len vents Adam, he grabbed his former friend's Advent Deck and released the Advent Beast....He threw the blank Advent Deck into the portal to Earth as Mirror Monsters cornered him in Xaviax's palace.

Kit is also the only one to stumble onto his Advent Deck, as opposed to Xaviax handing it to him. It's all probably related.

My theory is that Adam has a corrupted version of the original Dragon Knight deck since he is corrupted himself.

Thus Kit couldn't have a deck that is already contracted.

How then does this deck even exist? You know, if we're working under the assumption the Advent Decks Xaviax has been handing out each belonged to the Warriors of Ventara before they were vented.

You shouldn't try to compare apples and oranges.

Kit got his Advent Deck from his dad.

Xaviax is handing out the Advent Decks used by the original Ventaran Kamen Riders, that isn't an assumption they flat out said it.

So we're thinking. Len is convinced Xaviax had a hand in that, too.

Xaviax does it in person, Kit was told about the dragon and to go home (so he could get the deck) by a ghostly image in the mirror. Xaviax didn't do it. Kit's father's disembodied soul did.

I like your theory Decade, I've been wondering why Kit's was the only person whose deck was just laying around earth. Especially if Adam betrayed the original knights, Xaviax should have been in possession of his deck.

Also...someone has to be the black Dragon Knight.

Definitely is.

THEORY: The Dragon Deck that Adam had is the Black Dragon deck. Corrupted by Xaviax of course.

As to Kit's father appearing in the mirror... I guess all of that depends on whether or not General Xaviax's ability to change shape goes beyond the two forms we've already directly seen.

As to why Dragon Knight's Advent Deck doesn't have a contract, that something I've wondered as well. Maybe just to sell a "Blank Knight" toy. Maybe Dragon Knight is unique amongst other riders (even Onyx?). And why is it that Xaviax orders both Torque and Strike not to vent Dragon Knight? Maybe someone who has seen Ryuki knows, but I don't. Unless Xaviax thinks that once Wing Knight is out of the picture Kit will just give up and join him. But then why does Strike say "I'll save you for later"?

He wants Wing Knight out of the picture because he is the bigger threat. Dragon Knight is a nobody he can take his leisure with him as he sees fit.

I think its more then that. Xaviax seems to have a plan for Kit. And is perhaps decieving him somehow. Dragon Knight is key to his plan. Just like Adam was before Kit. This should be come aparent down the line.