優は最近太り始めたネガの減量作戦を開始した。だが、ネガは太ったのではなく、カゼを引き、クシャミのたびに大きくなっていたのだ。このままではどんどん大きくなってしまう。あわてたママは病院へ連れていくが、正体がバレるのを恐れたネガは逃げてしまった。優はネガを探す途中で、薬草を取ってきた守と出会う。
Even though he is not thrilled with having to participate in the subterfuge necessary for Yuu to manage her double life as Creamy Mami, Nega finds it no trouble at all to conduct himself like a carefree housecat -- a lifestyle that he is starting to pay for when he contracts a cold that causes his body to expand with every sneeze. Nega's speculation with Posi about why Earthlings contract illnesses that are unheard of on the Feather Star prompts the offended Yuu to offload Nega out of her cowl as she decides him a strict exercise regimen. The next morning, Yuu is shocked to find that Nega's ailment is not the straightforward matter of excessive corporeal mass it appears to be; while Yuu desperately taps Toshio and Midori for answers, Natsume panicking over Nega's deteriorating condition brings things to a head when a veterinarian decides to X-ray Nega. The skeleton key to the whole three-ring circus to secure Nega's survival from both the cold and dissection ultimately rests with Mamor
