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Rules of Kyudosudoku

Kyudosudoku is a logic puzzle that combines Kyudoku with variety Sudoku.

Each puzzle consists of four 6×6 grids filled with digits 1–9 — the Kyudoku grids — and a blank 9×9 grid, the Sudoku grid, often with some extra graphics in or around it.

The Kyudoku part

In each Kyudoku grid, exactly one of each digit 1–9 must be circled in such a way that the circled digits in each row or column never add up to more than 9.

	Invalid: two 2’s are circled.
	Invalid: none of the 4’s are circled.
	Invalid: the last column has 2 and 8 circled, which add up to 10, which is more than 9.
	Valid example.

The Sudoku part

The Sudoku grid must be filled with digits 1–9 in such a way that every row, every column and every outlined 3×3 box contains the digits 1–9 exactly once.

Furthermore, each Kyudoku grid is linked with a 6×6 “corner” of the Sudoku grid (the coloring helps to visualize this). Every circled digit in a Kyudoku grid transfers that digit to the equivalent location on the Sudoku grid, as shown below:

Note that the same is not true in reverse. If a digit you place in the Sudoku matches the corresponding digit in a Kyudoku grid, it does not necessarily follow that the digit must be circled. Similarly, a crossed-out digit in a Kyudoku grid does not necessarily imply that the corresponding Sudoku cell can’t have that digit in it.

Each Kyudoku grid in isolation may not have a unique solution, but there is only one way to solve the entire puzzle.

Variety Sudoku constraints

Each puzzle may have additional graphics in or around the Sudoku grid, which represent additional constraints that must be followed in order to arrive at the correct solution.

These are explained in-game with a tooltip (which you can turn on and off by toggling the tooltip button).

Complete list of variety constraints

Controls

Keyboard

Arrow keys	Moves the selection within the Sudoku grid.
Shift+Arrow keys	Extends the selection within the Sudoku grid.
Ctrl+Arrow keys, Ctrl+Space	Can be used to select multiple cells that may not be contiguous.
Z	Switches to “normal” mode: full-size digits are entered into the Sudoku grid. Use this to enter digits that you have fully deduced.
X	Switches to “corner” mode: multiple digits can be notated in the corners of Sudoku cells. This is usually used to notate which cells within a 3×3 box a digit can go.
C	Switches to “center” mode: multiple digits can be notated in the centers of Sudoku cells. This is usually used to notate the possible digits for a particular cell.
Q	While hovering the mouse over a Kyudoku cell, circles that cell.
W	While hovering the mouse over a Kyudoku cell, crosses that cell out.
E	While hovering the mouse over a Kyudoku cell, removes the circle or cross.
Ctrl+Z or Backspace	Undoes the last change.
Ctrl+Y or Shift+Backspace	Redoes the change last undone.
Escape	Removes any selection or highlight.
Digits	When one or multiple cells in the Sudoku grid are selected, the digit is entered into the cell according to the current mode (normal, corner or center). When no cell is selected, all occurrences of the digit in all grids (except for those crossed out in Kyudoku grids) are highlighted.
Ctrl+Digits	Enters a digit in center notation.
Shift+Digits	Enters a digit in corner notation.

Mouse

Click (Kyudoku cell)	Cycle unmarked → crossed out → circled
Shift+Click (Kyudoku cell)	Cycle unmarked → circled → crossed out
Click and drag (Sudoku cell)	Select any number of cells.
Shift+Click and drag (Sudoku cell)	Add any number of cells to the selection.

Common strategies

To get started, here are some common deductions that can help you get started on a Kyudosudoku puzzle:

	There is only a single 6 in this Kyudoku grid, so it must be circled.
	All values in the same row or column that would bring the sum above 9 can now be crossed out.
	All of the 1’s in the grid are in a row or column with the highlighted 9. This means the 9 can be crossed out because circling it would rule out all of the 1’s.
	All of the remaining 9’s are in the same column. No matter which one ends up getting circled, the other digits in the same column would bring the column’s sum above 9, so they can all be crossed out.

	Remember that the 6 we circled is transferred to the Sudoku grid. Any 6 in the other Kyudoku grids can be crossed out if it would place another 6 within the same row, column, or 3×3 box of the Sudoku grid.
	Similarly, this 8 can be crossed out because we now know that the corresponding Sudoku cell is already a 6.
	However, these 6’s cannot be crossed out (nor circled) as they correspond to the exact same cell in the Sudoku grid. Transferring the same digit into the same Sudoku cell multiple times is allowed.

These strategies should get you through some of the easiest puzzles. For some of the harder puzzles, many more advanced strategies can be discovered.

Enjoy!