Kakomu is a two-player game on a 5x5 grid of squares.
Players alternate placing X's and O's inside of the squares.
If a piece is directly surrounded on opposite sides, horizontally, vertically, or diagonally, by opposing pieces, that piece becomes a block.
If a sequence of allied pieces is directly surrounded by opposing pieces, all of those allied pieces become blocks.
Existing blocks prevent capture.
Capture occurs simultaneously for all pieces involved, even the most recently placed. In the third board below, an O has been placed on the second square.
The board wraps, horizontally, vertically, and diagonally.
An entire row of pieces, such as two X's followed by three O's, can be captured at once, because the X's and the O's simultaneously surround each other.
However, a single piece cannot capture, so an X followed by four O's, for example would simply get captured without doing any capturing itself.
The game ends when there are no more unmarked squares.
The player with the most pieces on the board is the winner. X wins in the example above.