With Sayako and Toune trapped in the castle of Lucky Thoroughbred, Bocca and Koko sneak in to save both. While on the way in, the two get more than a bit comfortable with each other, and Coco tells her story to the boy. Within the castle, a helpless Sayako is reminded of her old family, and of her brother's "achievement" to become a Monster Union agent. Meanwhile, the two Melos Warriors go separate ways. Bocca eventually meets up with Lucky Thoroughbred, agreeing to a race with his robot monster over a lake of water, since if Bocca wins, his friends would be released. At the same time, Koko in off saving Toune, when met up with Flying Bunny, where trouble starts to occur. What happen there? And can Bocca win the race with his flightless Aibar-Machine?
モンスターユニオンに捕らえられてしまった小夜子を探していたボッカ。
その途中偶然に、ココら「チェンタウロ」のメンバーと再会する。
そしてボッカはココと二人だけで、敵の「水門塔」に進入する事になるのだが・・・
