Actually it was more about the artists in the single which are already related to anime, both of them. And adding their unit group CaoCao, would be a more info on both.

Second reason would be, and i thought it was okay :/ , was adding the single main theme as it was not released with the soundtrack. :/

edit:
my purpose was gathering that info in here, since ... they are already here. why not?
it took me some days, to find anything about who the hell CaoCao was , but they only existed for this single

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