Wonderful things come in small packages, and this one tucks nicely into your character's pocket. It has been so lovingly crafted and carefully boxed so as not to be damaged...what possible reason could your character have for carrying such a thing?
And Kimono Princesses sometimes wear jewelry. (There's actually a reason Japanese women don't have a big history of wearing rings, necklaces and pins – kimono fabrics were often more costly than jewels, and nobody wanted to risk something snagging or AI YI YI putting a hole in the priceless fabrics. But new style kimonos aren't expensive – most of them are vintage – so even cheap costume jewelry is safe to wear.)