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Momoi is one of the students studying in Millennium Science School.
She is the scenario writer for the Game Development Dept. at Millennium. Both she and her younger twin sister, Midori are literally developing video games in the Department.
Although her cheerful personality are polar opposite for her shy sister, but their passion for games are strikingly similar and become great partners.
(Source: Sensei! Welcome to Kivotos! Wiki)