Ukai is a historic form of fishing at night on rivers in Japan, using cormorants to dive for fish. The fish caught are usually ayu (sweetfish). A rope on the bird's throat stops them from swallowing the fish they catch. Once they have caught enough fish for the fishers, the birds are fed.
The most famous location for Ukai in Japan is on the Nagara River (Nagaragawa) in Gifu province. The fishing people go out in long wooden boats, with a large wood fire raised up on the boat to light the way.
In this game, players move up the river, a tableau of cards laid face down. As the fishers move up river, the diving birds reveal cards. Some have sweetfish (1 to 5 points), others have hazards, such as the bird striking a rock. Some cards have special effects too. The game ends when all the 'bonfires' in the game are exhausted, meaning time is out. The player with the highest score in fish is the winner.
The game is published in a tiny matchbox box (no striker), with a deck of small cards and includes matches. It was recently shown on Twitter as the smallest doujin game in Japan.