Older generations of Japanese would likely have fond memories of watching fireflies, called hotaru, in the early summer. Nowadays, with massive urban development, fireflies are disappearing. Only in pristine environments can you still find these magical lights.
At Kinchakuda, the fireflies disappeared for a period of time but with the help of a firefly expert, the fireflies returned. There is a roped off sanctuary where the fireflies still thrive in late May to early June (crossing over the roped off area is prohibited). During this brief period, the Hidaka City Government lights up the path around the sanctuary but firefly appearance is of course not limited to this period only.
Watch the fireflies flit along the banks of the stream and among the reeds. If you're especially lucky, they just might land on you. Visitors are requested not to use flash when taking photos of the fireflies. Taking the fireflies home is also prohibited. Read more about the fireflies in Kinchakuda here.
From Koma Station, Kinchakuda is about a 10 minute walk. Many parking spaces are available. If you are coming by car, tell the staff at the guide tent that you intend to go to the firefly event.