Although she should be happy about its effect on the family micro-economy, the diurnal heat and a mob of impatient customers drives Natsume batty as she tries to entreat Tetsuo to take the family on a seashore vacation citing the effect it is having on Yuu who daydreams about swimming in the ocean before Nega snaps her back to reality as he and Posi prosecute an analytical concourse over the logistics and consequences of Yuu taking a vacation from her double life as Creamy Mami -- an incidence of which is that day when she has it explained that she is to conduct a joint concert alongside Megumi as Creamy Mami at Isohama complete with a brand-new high-tech mobile production van; later that evening, Yuu throws a temper tantrum in an attempt to defeat her earlier »gung-ho« exhibition about working while pointing out that Natsume was trying the same thing earlier only to have the annoyed Tetsuo affirm some very decisive family government. The road trip to Isohama the next morning becomes the forum for Yuu to ultimately learn the lesson »Be very careful what you wish for« when Natsume engages Shingo in a dangerous road race en route to the beach; if that is not enough along with the hefty workload of preparing crepes alongside Toshio and Midori without Natsume and Tetsuo to lead them through it, Yuu finds that doing her thing as Creamy Mami takes on a whole new dimension when she has to perform the joint concert not with Megumi but with her magical alter ego.

磯浜ビーチでマミとめぐみのジョイントコンサートが開かれることになった。2泊3日の予定と聞き優は困るが、両親にダダをこね磯浜ビーチへ連れていってもらう。コンサートの夜、めぐみはマミを困らせようと、素人デュエットを企み優を指名。驚く優だが、スモークにマミのフィルムを映しデュエットを無事に歌いこなした。