"Happy Days" is Ai Otsuka's fourth single. The title track was used as background music in the Morinaga ICE BOX CM, which starred Otsuka, and as the theme of Koukousei Quiz 2004 on Nihon TV. It also contained a new b-side song "Hoshikuzu" (ๆใใ) and instrumental versions of both songs. Number three Oricon charts.
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