Following Apollo Geist into another A.R. World, Decade is attacked by Kamen Rider Black until Diend arrives and summons Femme to hold him off. The next day, after learning that he is in the World of Black and seeing that he is on his own in saving Natsumi, Decade ambushes Guy as Ryuki and fights him until he uses a little girl as his hostage. When Decade takes a hit from Diend to save the child, Black watches and has second thoughts about him as Apollo Geist escapes. After explaining that Apollo Geist came to the world before and recruited the cult Gorgom into Dai-Shocker, Kotaro reveals that Joe the Haze ended up in his world and has been helping him fend off Dai-Shocker's endless army. Schwarian arrives and sends the Scorpion Imagin and Mantis Fangire after Decade and Black. Using Faiz's power, Decade destroys the two monsters as Schwarian summons the Chaps, allowing Tsukasa to make it back to World of Black RX as Apollo Geist summons a pack of Orphnoch and Worms. The numbers even out as Daiki arrives and use Decade's card to summon the World of Black's Kotaro. With Black and Black RX fighting with them, Decade and Diend battle the monsters as Decade assumes Complete Form and uses Agito Shining Form's power to destroy Schwarian. After getting the Perfecter from Apollo Geist, Diend steals it as Yusuke arrives to tell Tsukasa that Natsumi is about to die. Once there, Daiki shows up to give the Perfecter to Tsukasa, who uses a bit of his life force to revive Natsumi and bring her back to life. Black and Black RX continue their battle Apollo Geist until he is escapes into another A.R. World with Narutaki comments that Decade is to blame for Dai-Shocker. After checking up on Kotaro and telling him that Joe is aiding his other self, Tsukasa returns to the Hikari Studio where he and his friends venture into the next world.[27]
BLACKの世界。アポロガイストを追ってBLACKの世界に来たディケイドは、もう一人の南光太郎に会う。南光太郎によればアポロガイストの取り持ちでゴルゴムと大ショッカーが手を組んだという。キングストーンの力でRXの世界に戻ったディケイドは、RX、ディエンドが召還したBLACKと共に闘いに挑む。
