第1話: 帰還先住所の記載漏れにもかかわらず、6ユニットが希少なU4 Fes音楽祭に参加

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The six units are introduced at the Unknown Underground Unbelievable Ultimate Fes. (U4 Fes.), a mysterious music festival that takes place once every 100 years. Happy Around! receives its invitation in the mail, and although the four agree to participate, Rei notices the lack of a return address. (Source: Wikipedia)