The enemy 'Komayto' is a reference to the Metroids in Metroid, a game that uses the same engine as Kid Icarus, and was released on the same day. As well as having the same appearance, the name comes from Kometo, short for Kometoroido, which means 'Metroid Child' in Japanese.
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In the instruction manual the enemy "Siren" is shown naked with breasts, including nipples.
The majority of Kid Icarus was developed during three months of intense work, where developers would stay up all night, and sleep in the office. They created make-shift beds using cardboard boxes and curtains, and would endure hours of winter cold in the unheated building.