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While explaining her reason to Hayate, Chiharu says the following quote: "A lesson that is not accompanied with pain has no meaning". This was used by the character Alphonse Elric from the series FullMetal Alchemist.
On the news section of the website Nagi was managing, it mentions that Niwa Niwa Douga was showing all the episodes of Mawaru Nyankodrum. This is a reference to the website Niconico (formerly Nico Nico Douga) and the anime seires Mawaru Penguindrum.