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These all reference reference the 1988 Tokusatsu show "Dennou Keisatsu Cybercop", which tells the story of the Z.A.C, a special police unit called the Jupiter Unit, led by Shin'ya Takeda.
The mail even includes a reference to character Tomoko Uesugi, a backup Z.A.C officer who was supposed to be the Venus Unit, but whose armor wasn't made due to financial issues.
Since the item you get for replying to the mail is the Venus Armor, the game seems to suggest that the heroes of Chroma Squad are the ones who end up with Tomoko's suit.
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