Just about every culture has their trickster myths. In Japan, there are plenty.
The ghosts all tend to be mischievous. Animals transform themselves into humans at whim, playing us bipeds for fools. The Tanuki (raccoon dog) unquestionably reigns supreme among all the tricksy beasts and beasties.
Nearly forgotten among the various tanuki stories is the Mame-Danuki 豆狸, or the "bean-tanuki". This Yokai (a type of spirit or mythical critter) could inflate it's testicles (don't ask me how, I'm really trying not to think about it too hard) to monstrous proportions. It then uses them as an umbrella on rainy nights. Or just about anything else you can think of.
As depicted here:
Seriously. Check that page out if you dare. I haven't laughed that hard in...maybe ever. For my money, the catfish is the best. Pick your fave.
I would have gone merrily on my way through life, not knowing of the wonder that is the Mame-Danuki, if my wife had not picked up a great little Yokai Origami book for me recently. It's done by the design team Cochae, and is fantastic. As soon as my astonishing wife saw the Mame-Danuki, she made me promise to create one to add to my growing Yokai collection.
Incidentally, "Kintama" [ 金玉 ] is the Japanese word for testicles. It translates literally as "golden balls", illustrating the level of importance placed on the little guys.
My floating friend here is using his to drift softly down to earth, a kind of "golden parachute". I will leave it up to you to decide if he should have remained forgotten.