What's this alluding to?

What's this alluding to?

Early on in the series, Kyouko gives everyone in the Amusement Club a set of pajamas (including herself, with the Tomato pajamas). Yui's is a panda, and presumably Kyouko took it and replaced it with that frilly set of pajamas.

Give her back the panda

By the way, Kyouko's pajamas are the only non-animal ones.
She also gets pajamas for the student council in Nachuyachumi, and she's still the only one not to have animal ones.

I vaguely remember this. This whole thing was a challenge or some sort that Namori did. I can't remember the details. It's been a while ago...