Psacothea hilaris hilaris (kiposhi-kamikiri キボシカミキリ in Japanese) / Japanese longhorn beetle
Kamikiri means paper-cutting or chewing it gets its name from the way the bug lays its eggs: The female kamikiri-mushi chew chunks of wood, make deep tunnels and lay a few eggs within. Right now, forests that have many species of trees are disappearing from Japan. So kamikiri-mushi are having a hard time living surviving and many of them creep into people’s gardens and chew up people’s trees (this is from my Japanese bug book).
There are many kinds of kamikiri longhorn beetles in Japan see this page for photos of the different colored ones, bright red or blue ones.
The bug in the photo below looks a lot like the kiposhi kamikiri-mushi or longhorn beetle but perhaps a different species.