Many Audax clubs, including those in Japan, prohibit use of flashing lights on bicycles. Indeed, German and Netherlands law prohibit flashers. Some other places also prohibit them (or at least prohibit a bright, flashing, front light that will bother drivers). Audax clubs also require that lights be affixed to the bicycle frame (except, perhaps, one on the rear of the helmet).
This article on the Bikeradar website summarizes current research on whether flashing or solid lights are safer, and suggests that the Audax rules may be out of date.
https://www.bikeradar.com/advice/buyers-guides/flashing-bike-lights/
One key piece of research emphasizes the importance of lights, and reflectives, on moving parts of the body -- the legs and arms, and less so the head.
"The study found that when steady lights were mounted to the cyclist's pedaling heels, participants [identified the cyclist] from a mean distance that was 1.7 times greater than when a flashing light was mounted to the seatpost. This figure increased to 5.5 times when compared to a steady light mounted to the seatpost."
Some Audax groups (in the US) do require reflective ankle bands. Those in Japan do not ... but should.
And the Japan clubs also should allow flashing rear lights, and encourage use of lights on the heels or ankles.
