Shiro Kenzaki had created the Rider War in order to keep his sister alive. However, the ones seen in Ryuki weren't the only ones of their kind. Now a few...prototypes have found their way into the Worlds, and the original Riders there...are surprised at the appearance.
List of Riders
Kamen Rider Ryuki: Eddy Nanbu.
Kamen Rider Knight: Eddward "Double-D" Browning.
Kamen Rider Scissors: Kevin (Ed, Edd, n Eddy).
Kamen Rider Zolda: Ed Loveless.
Kamen Rider Raia: Rolf (Ed, Edd, n Eddy)
Kamen Rider Gai: Michael; Jimmy (Ed, Edd, n Eddy)
Kamen Rider Ohja: Shinji Ikari (Evangelion)
Kamen Rider Imperer: Ross (RWAF-Self)
Kamen Rider Tiger: Ranma Saotome (SRW-Verse)
Kamen Rider Femme: Nazz (Ed, Edd, n Eddy)
Kamen Rider Ryuga: Terrence Kerr (Blood Lord Dark Kiva)
Kamen Rider Verde: Jonny 2x4 (Ed, Edd, n Eddy)
Kamen Rider Odin: Andrew (wildrook)
Kamen Rider Abyss: Tsukasa (Decade)
Kamen Rider Alternative: Yuusuke (Kuuga)
Kamen Rider Alternative Zero: Tsukune (Rosario + Vampire)
Dragredder and Dragblacker
Also known as the Twin Dragons, they happen to represent Ryuki and Ryuga, respectively. Instead of just being two different halves, the both of them are separate entities.
Dragredder's human identity is Gwen, which is short for Gwenivere. Her contracted Rider is Eddy Nanbu. Unlike her darker twin, she has a good heart and can be flirty to him when the moment arises. She does care about him and hopes that Eddy doesn't suffer the same fate as the original Ryuki (Shinji Kido) did.
Dragblacker's human identity is Rin, which could be either the original Kamen Rider Knight or the girl accompanying him. She keeps a firm opinion that it's not the power that corrupts, but how it's used, so she holds a bit of disdain for Shinji's mirror counterpart. Her contracted rider is Terrence Kerr, and Top Galer usually shows his perverted side when she's around.
Despite the name, she's not really evil. She's also been around longer than the others because of the cultures of a certain Son of a Shepherd, who happens to be her current contracted Rider. Surprisingly enough, she's well liked there because of their fish customs. Her human identity is Eva, which, in some cases, would be short for Evil (as in Deliver Us from Eva). She's also best friends with Gwen.
Despite being Odin's contract monster, she's actually kindhearted and wise. A little on the sneaky side, but when she makes a promise, she keeps it. Oddly enough, she's a good friend of Seig's, which makes it less awkward with the Taros group. Her contracted Rider is Andrew, who was a little concerned about the mind-control issue that pops up sometimes. Her human identity is Suzaku, which is known as the Red Phoenix of the South, the red part being the color of his Advent Deck.
Ohja's Contract Monster. Despite being a little on the poisonous side, she actually cares for her Contracted One because he was a psychological mess. Her human identity is Natasha, oddly enough. She also dislikes Gendo Ikari because of the abandonment, but then again, who doesn't?
She also mentioned that she would become Genocider, but was it worth the risk...
Out of all the Contract Beasts, Gigazelle happens to come in packs. Human Identity happens to be known as Tanya while her Contracted Rider...is Ross from the Real World. Imagine the look on his face when he found out that she was the pack leader of the group of Gigazelle.