Bocca and Sayoko arrives at a tourist spot. Sayoko's investigation into the place reveals that several tourists have gone missing there. They spot the body of Tone's Aibar machine, Skyblue, the blue eyed boy, lying close to the waters. Bocca revives him with the aid of his Aibar machine. They learn that Tone has been taken prisoner at a castle managed by a member of the Monster Union known as Lucky Thoroughbred. Skyblue suddenly warns them that they had been spotted and that the enemy was headed their way. Flying Bunny, a girl in a bunny costume riding a flying board, arrives. Bocca, Sayoko and Skyblue are spotted by her. She goes on an aerial attack. In the battle against Flying Bunny, Bocca's Aibar machine attempts to fly but is unsuccessful. Bocca successfully wounds Flying Bunny, and she retreats to the castle to heal herself. She meets with Lucky Thoroughbred and they exchange some harsh words. Lucky Thoroughbred reveals his intent to set bombs all over the world and then visits his captive, Tone.
Skyblue meanwhile, meets up with another Airbar machine, the one who uses boomerangs as weapons. They fight each other. Sayoko meanwhile tries to kiss Bocca, but Bocca hesitates. Sayoko learns why, she realizes that Melody is watching them. Sayoko runs off feeling hurt. She is suddenly greeted by Lucky Thoroughbred in his monster machine. Sayoko however, looks more surprised than afraid. And instead calls him, "brother".
「幸運河」にやって来るボッカと小夜子。
そこでは、たくさんの子供たちが何者かに誘拐されていた。
モンスターユニオンの仕業かどうか調査を開始するボッカ。
そんな時、河岸に一人の少年が流れ着いた・・・
