Those interested in netsuke may enjoy the book "The Hare With Amber Eyes" which weaves the story of a netsuke collection though generations and different continents.

This article would've really benefited from a photo or sketch of what one would look like when being worn.

Reminds me of phone charms and key chains (some Japanese key chains are fashionable and bulky extending from the pocket). Obviously, given there are pockets now they serve a slightly different purpose, but it's a similar niche. I wonder if there's a lineage there.

How come they weren't losing the boxes all the time? A string under the belt with only a small stone preventing it from sliding down seems unreliable.

I think the belt is tight around your waist, and then the netsuke is stuck above the belt. If you pull on the string it can't slide because there is no space for the netsuke to pass under the belt.

There's a picture here: https://www.netsuke.com/netsuke.html