A Medium 7×7 Puzzle Solved with Forced Chain in 13 Steps

This 7×7 board rates as medium (difficulty score 921). Solving it from scratch takes 13 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Paired regions, 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 column E, so its marker has to land there; that clears every other open cell in the column.
2. Next, every open cell left in this region sits in column A, so its marker has to land there; that clears every other open cell in the column.
3. Then, place a marker at B2. Region has exactly one open cell left. Placing here clears the rest of row 2, column B, and its region. Placing here also clears its 2 touching neighbours.
4. After that, every remaining candidate in this region touches E4, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
5. Now, place a marker at E5. Region has exactly one open cell left. Placing here clears the rest of row 5, column E, and its region. Placing here also clears its 4 touching neighbours.
6. From there, every open cell left in this region sits in row 3, so its marker has to land there; that clears every other open cell in the row.
7. Following that, together, two regions have open cells only in rows 1 and 4; with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
8. First, marking D1 would force G4 (the last open cell in region 3), and then row 3 would be left with no open cell for its marker. So D1 can't be the marker there.
9. Next, place a marker at C4. Region has exactly one open cell left. Placing here clears the rest of row 4, column C, and its region. Placing here also clears its 1 touching neighbour.
10. Then, place a marker at F3. Region has exactly one open cell left. Placing here clears the rest of row 3, column F, and its region.
11. After that, place a marker at G1. Region has exactly one open cell left. Placing here clears the rest of row 1, column G, and its region.
12. Now, place a marker at D7. Region has exactly one open cell left. Placing here clears the rest of row 7, column D, and its region.
13. Finally, place a marker at A6. Region has exactly one open cell left.

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