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Hotaru Beam is a Nikoli puzzle in which the aim of the game is to connect the circles on the grid through a single, continuous network. It's a very straight forward puzzle, but depending on the hints that are given it can take a while to figure out the right solution.

Hotaru Beam can be played on any sized grid, but the bigger the grid the more difficult the game becomes, assuming you increase the amount of circles with the size of the grid of course.

The rules are as follows:

- All circles have to be connected through a single network.

- The beam (line) coming from a circle can only start from the little circle on one of its sides.

- The network of beams cannot branch out and cannot cross itself.

- The numbers in the circles indicate how many turns the beam will make to get to the next circle.

- Turning at a corner because there's nowhere else to go still counts as a turn.

- A circle's beam will only end in the side of another circle that doesn't have a beam 'projector' (little circle).

As mentioned, Hotaru Beam is a straight forward puzzle. With a little deduction work you can often figure out the solution in a handful of minute, depending on the difficulty of the specific puzzle of course.

In terms of finding a solution it's always easiest to start with any circle that has the number 0 in it. It will go straight and thus connect to the next circle. This immediately eliminates other paths that could've crossed this one, but since crossing paths isn't allowed those options are no longer available.

If there are no circles with 0's the next best thing is usually to find circles which are enclosed by other circles, meaning they have few ways to go before hitting another circle with their beams. However, simply tracing all possible routes for any a couple of circles and seeing if any of them could work together is often enough to reach the solution of that puzzle.

Hotaru Beam's a fun, but relatively straight forward puzzle to convert to an RPG setting. There are beams of some sort and there are elements these beams have to reach. So, those beams could be light sources, cosmic energy beams, a death ray that needs to be send back to itself, or perhaps a simple flow of water that needs to reach every house in the village.

For my example I went with an energy beam of sorts. My character is faced with a room of beacons. One of them has already been activated, which in turn gives the one it shoots power to activate as well. She's also been given mirrors, number clues and the instructions on how to solve a Hotaru Beam puzzle.

All my character has to do is put mirrors on the places where the beam has to turn a corner and direct it to the right beacon in the sequence. Once the entire sequence has been completed she'll be free to progress through a secret door that'll open up.

Should she fail to find the solution or if she crosses the beams at any point by activating a beacon too soon, she'll fail the puzzle and not be granted access to the secret door, which means no loot. The story will still progress of course, the solution to a puzzle shouldn't stand in the way of this.

There are plenty of ways to adapt Hotaru Beam, and they can be incredibly varied too. Some puzzles tend to be more suited for certain settings, like a futuristic one, but Hotaru Beam can usually be applied to all settings.