Kamen Rider Ryuki (2002)

Both Kamen Rider Agito and Ryuki share similarities in the dark tone and the mystery that surround the plot of the series.

Both shows are a battle royal of good and evil Kamen Rider that are fighting to win a wish/fruit

Both shows have over 10 riders (if you include the ryuki movies).

Both shows have a dimension from where the power originates

The rider suits all have motifs of warriors, which include knights and many others.

Both shows have about 10 riders. These riders fight each other and also work together, depending on the situation.

Both shows have a dimension besides the one where the riders live in

The riders of Saber are swordsmen/knights. The rider suits of Ryuki all have motifs of warriors, which include knights and many others.

Main rider of Saber has a dragon motif and many other riders have animal motifs as well. Main rider of Ryuki has a dragon motif and all the other riders have animal motifs. Both shows have a dark dragon motifed villain that fights the main rider.

(Kamen Rider Kuuga) Theme is Dark, it shows Kuuga evolving into a Rider and Ultimately didn't become what he was supposed to become and went on a journey to recover his smile. which is sad because he was such a happy go luck guy.

(Kamen Rider Ryuki)If you are looking for a Dark Drama with Mature Theme and you like to sob your little fangirl or fanboy hearts out, then this is for you my friends! I like it because it shows us all the dark side to us all with wanted to have a chance to fulfill a wish for a loved one or what have all the while you are fighting others and your inner self for the Final Wish at the end on that long and hard journey. The Finale will clearly satisfy those that truly love and stuck through the whole series! I liked it eventhough I shed some tears in the latter episodes.

Tokusatsu Heroes battling a survival deathmatch for a wish granted to the sole victor

Main character are both naive and friendly

Main characters motif are both dragons

You must fight if you want to survive.

Both shows focus on a group of characters given special items (a deck of cards and a VR headset, respectively) by a game master, who is prodding them to kill everyone else to receive a reward. With a lead character whose conscience is too strong to kill anyone.
Alternate worlds are present in both premises. Versus Road having VR and Ryuki having a world on the other side of the mirror, with both of them being the setting for (most of) the fights.

Both Kamen Rider Ryuki and Ex-Aid have several Riders fighting each other through competition and betrayal while facing monsters in their respective stories (Mirror Monsters / Bugsters). Both also have a secondary Rider with a knight motif.