When I first saw this tiny clearwing moth (sukashiba), I thought it was indeed a little wasp, but then I noticed it had a thick hairy body, so I realized what it was. Their defence mechanism is, of course, that looking like a wasp helps to protect them from predators.
There are about 40 species of clearwing moth in Japan, so I am not certain of my identification. However, it looks most similar to the pictures of Trichocerota constricta (munabuto-hime-sukashiba) on JPmoth. I was confused at first because it didn’t seem to have the distinctive forelegs of this species, but looking at the side view (picture 6), it is possible to see that the forelegs are tucked under the wings, and the middle legs are in the forward position.
Thank you to Professor Yutaka Arita (Meijo University, Faculty of Agriculture) for confirming my identification. He sent me an email saying that this is a female.
Trichocerota constricta = munabuto-hime-sukashiba
Location: On vegetation next to a pond (near Konominato, Fukuoka)