A Sharp 9×9 Puzzle Solved with Forced Chain in 22 Steps

This 9×9 board rates as sharp (difficulty score 1077). Solving it from scratch takes 22 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Shape squeeze, Forced chain. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
2. Next, every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
3. Then, every remaining candidate in this region touches G2 and H2, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
4. After that, every remaining candidate in this region touches F3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
5. Now, every remaining candidate in this region touches F6, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
6. From there, every remaining candidate in this region touches C6, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
7. Following that, marking G1 would immediately leave region 2 with no open cell for its marker, so it can't be the marker there.
8. First, place a marker at H1. Region has exactly one open cell left. Placing here clears the rest of row 1, column H, and its region. Placing here also clears its 1 touching neighbour.
9. Next, every open cell in row 8 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
10. Then, every remaining candidate in this region touches B7 and A9 and B9, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
11. After that, place a marker at A8. Column 1 has exactly one open cell left. Placing here clears the rest of row 8, column A, and its region.
12. Now, every open cell in column B belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
13. From there, marking B2 would force G3 (the last open cell in region 2), and then region 6 would be left with no open cell for its marker. So B2 can't be the marker there.
14. Following that, place a marker at F2. Row 2 has exactly one open cell left. Placing here clears the rest of row 2, column F, and its region. Placing here also clears its 1 touching neighbour.
15. First, place a marker at G4. Region has exactly one open cell left. Placing here clears the rest of row 4, column G, and its region.
16. Next, place a marker at B3. Region has exactly one open cell left. Placing here clears the rest of row 3, column B, and its region.
17. Then, place a marker at I5. Region has exactly one open cell left. Placing here clears the rest of row 5, column I, and its region.
18. After that, every open cell left in this region sits in column E, so its marker has to land there; that clears every other open cell in the column.
19. Now, every remaining candidate in this region touches D6 and D7, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
20. From there, place a marker at C7. Region has exactly one open cell left. Placing here clears the rest of row 7, column C, and its region.
21. Following that, place a marker at E6. Region has exactly one open cell left.
22. Finally, place a marker at D9. Region has exactly one open cell left.

The key move here was Forced chain. Once you can spot that, this board falls quickly. ∎