As you can see in the 4th picture, these “pleasing fungus beetles” (oo-kinoko-mushi) are gregarious, perhaps even pre-social. In total, there were more than 50 adults on this tree. You would think that such a distinctively patterned beetle would be easy to identify, but that’s not the case because there are several very similar beetles in another genus (Megalodacne). I cannot be certain that I have identified this species correctly, so I shall wait to be corrected.
Coleoptera: Erotylidae (Pleasing fungus beetles)
Episcapha fortunii (I think!)
Location: In orchards and bamboo/pine forest above Yokoyama Village (Google map)