Hotaru Beam (lit. 'firefly beam') is a binary-determination logic puzzle published by Nikoli.
Hotaru Beam is played on a rectangular grid, usually of dashed lines, in which numbers in circles appear at some of the intersections on the grid. Additionally, each circle has a dot on one of the grid lines leading into the circle.
A circle with 0 on it (not the same as a blank circle) is a given: It will have at least one line going straight in the direction of the dot until it hits another circle. Each circle will have a line coming out of it in the direction of the dot. Since turning at the corner of the grid counts as a turn, a 1 circle near the corner may be forced to simply continue along the edge of the grid.