Apparently this is used as a uniform.
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Artist's commentary
AI-ko and Roboko and Bunny Day
"AI-ette", "Robo-ette"
Aug 2 = Bunny Day. From goroawase "Ba" (8) and "Ni" (2).
There are also two other "Bunny Days", on Aug 21 ("Banii") and Aug 23 ("Bani-san").