Santoitchi is yet another genre involving trominoes. The name seems to mean Three-and-One in Japanese with a deliberate misspelling (イッチ instead of the usual イチ for "one").
Here is an example puzzle with solution:
- Shade some cells. The shaded cells are not allowed to share an edge.
- Divide the unshaded cells into trominoes (contiguous group of three cells).
- Each tromino must contain exactly one number.
- The number indicates how many shaded cells share an edge with the region. (Not to be confused with "how many edges of the region are shared with shaded cells")
Now solve the following puzzle. A question mark represents one number between zero (inclusive) and infinity.
Sorry for puzzle change. This one is designed around a "key deduction" I had in mind. However, shortly after posting the original puzzle, I realized that there's a rather trivial, unintended solving path. The revised one eliminates the trivial path (hopefully; at least I checked but couldn't find any) and will force you to find the "key deduction".