Manju is a type of steamed bun with a filling. Typically the description of the filling is shortened so that a meat (“niku”) manju is “niku-man”, red-bean paste (“an”) is an-man, pizza sauce is “pizza-man” etc etc.
“Panda-man” is chocolate cream flavoured, “panda” refers to how it looks, not the contents. Needless to say this offends my sense of propriety, something that amuses Kei.