(I'm so, so sorry.)

hakoiri musume is an old Japanese phrase that literally translates to "daughter in a box." It is a metaphor for a daughter brought up with extreme care, with positive/negative implications varying by speaker and era as you might expect.

Since it's such a vivid visual metaphor, it remains a very popular gag caption for photos of daughters, girls in general (musume can also just mean "girl" or "young women"), and especially pets, in cardboard boxes.

It's also the name for a family of Japanese sliding-block puzzles, popular since at least Edo times, where the object is to manoeuvre a gigantic and awkward "daughter" piece past her relatively dimunitive yet closely packed family and servants to freedom. Representative applet.

I note in passing the mysterious and wonderful poetry of "Royal Out Game" as an English name for this puzzle, although I'm sure that there was an isometrically equivalent European version with its own lineage and backstory as well.