Kamen Rider Ryuki: 13 Riders The Comic is a manga adaptation of the TV special Kamen Rider Ryuki Special: 13 Riders published by Monthly Shonen Ace in November of 2002 and reprinted for Kadokawa on January 16th, 2003. The manga was done by MEIMU[1]. While a faithful adaptation, it does diverge by giving different multiple endings than those seen in the TV special.[2].
Shinji doesn't receive a list of the Riders' names and locations from Sakakibara, but rather learns them from Yui.
Kitaoka actually collapses in front of Shinji while walking to his car and has to be helped the rest of the way by Goro.
Verde first appears disguised as Knight and only reveals his true identity after mortally wounding Raia.
Takamizawa, Kitaoka and Jun aren't the only ones who approach Ren to form a temporary alliance against Shinji. Seven people are shown total, including Miho and Asakura.
Scissors is never killed by Ouja and survives to participate in the final battle.
Gai isn't killed by a Mispider during the final battle.
Shinji is shown to be the final winner in the initial ending where he faces the surviving Riders as Knight. There's some indication that Shinji has lost himself in carrying out Ren's will and can't even recall whether he is actually Ren or it was a name entrusted to him.
Ren doesn't die in the alternate ending and ultimately gives Shinji the go-ahead to destroy the Core Mirror, which is depicted as a cube floating high in the air. Ryuki Survive uses Shoot Vent to destroy it. The reset which results is nearly identical to the one in the last episode of the series proper, though in this case, Jun and Takamizawa (Verde) appear but Tezuka does not.