Sashimi X-Wing Sudoku Technique

Updated 11 August 2026

A Sashimi X-Wing is a finned X-Wing where one of the two base lines is missing its normal second corner candidate entirely, leaving only a single cell there, yet the pattern still forces the same kind of eliminations as an ordinary finned fish.

When a Sashimi X-Wing applies

An ordinary finned X-Wing keeps both base lines close to the plain X-Wing shape: each line has its corner cell inside the two cover lines, and one line has an extra fin outside them. A Sashimi X-Wing goes one step further by letting a base line drop its corner cell in one of the cover lines altogether, so that line contributes only one candidate cell rather than two. The missing corner is “cut away”, which is where the sashimi name comes from.

The two-branch argument still works. One base line supplies exactly one candidate inside the cover lines. The other supplies a candidate inside the cover lines plus a fin outside them. Whichever way the digit actually falls — at the lone cell, at the other line’s cover cell, or at the fin — any cell that shares a unit with the fin and also sits in a cover line is ruled out, for the same either/or reason as a regular finned fish.

Worked example

In row 9, the only cell left that can hold 1 is r9c5 — the cover-column-5 corner, with no candidate at column 7 at all. In row 6, 1 is a candidate at r6c7 — the cover-column-7 corner — and also at r6c6, a cell outside both cover columns. That third cell is the fin. Because row 9 is missing its column-7 corner, the base lines only supply the digit through r9c5, r6c7 and the fin at r6c6, rather than the four-cell rectangle a plain X-Wing would need.

r6c6 sits in the same box as r4c5 — both fall in the middle box that spans rows 4 to 6 and columns 4 to 6. r4c5 was carrying 1 and 9 before the deduction. Whichever cell in the base lines actually holds 1, r4c5 cannot, because it shares that box with the fin, and the fin is the only base-line candidate that reaches outside the two cover columns. The solver removes the 1 and leaves 9 behind.

How to spot a Sashimi X-Wing

1. Look for a base line with only one candidate cellFind a row or column where a digit’s only remaining candidate inside a would-be pair of cover lines sits at just one of them, not both.
2. Find the other base line’s corner and finIn the second base line, confirm the digit has a candidate at the matching cover line plus exactly one more cell outside the cover lines — the fin.
3. Check which cells share the fin’s boxLook at the cells inside the cover lines, outside the two base lines, and keep only the ones that also share a box with the fin.
4. Eliminate the digit thereRemove the digit from that narrower set of cells. The missing corner does not widen the elimination; it only changes how the base lines are justified.

Common mistakes

• Requiring both base lines to have a full corner pair. A Sashimi fish is defined by one base line having only a single candidate cell in the cover lines.
• Forgetting to check the fin’s box against the elimination target. The missing corner does not change that requirement; it is identical to a regular finned fish.
• Confusing a Sashimi X-Wing with a plain finned one. If both base lines still have a full corner pair inside the cover lines, the extra cell is an ordinary fin, not a sashimi cut.
• Assuming the missing corner means the digit is already solved for that line. It only means the digit has one home there among the cover columns; the line may still carry the digit in other, unrelated columns.