豪華客船で開かれるマミのコンサートへ来た優たち。あまりの人込みで皆とはぐれてしまったネガはアメリカから来たキャサリンという女の子に助けられる。彼女は日本に住んでいた頃庭に埋めた、夢を映す小箱を取り戻すために船から抜け出してきたのだ。箱を探し出した2人だが・・・。
A stampede of zealous fans eager to greet Megumi who is to perform a concert on the oceanliner being maneuvered into the port in preparation for docking means bad news for both Posi and Nega as the two cats are lost in the lurch during the hullabaloo; while Nega divides his energies between nursing his headache and getting his bearings as he computes his next move, a girl named Catherine successfully makes her escape from the ship much to her nanny's frustration. After explaining her prologue and her objective for being in Japan, Catherine sets course for her childhood home with Nega who tries to explain Posi the situation he is in; while Nega enjoys Catherine taking care of him in spite of the rough ride, Yuu is forced to suspend the search when it comes time for her to do her thing as Creamy Mami. The magic dream box now in hand thanks to some well-timed moves and cooperative circumstances, the problem now becomes how to smuggle Catherine back in under the nose of her very frustrated
