Gekitai is played on an initially empty 6×6 board. Each player has 8 offboard , which they take turn to onto the board on any empty square.
A newly dropped unit will push adjacent units, unless there is another unit in the way behind it. Units pushed off the board are removed.
So if Player 1 were to at b2 in this board state...
...then this would be the result:
Both a1 and a2 were pushed off board, and b3 was pushed to b4. c2 stays put since d2 blocks the push.
After a drop we check for the following in order:
winline
allout
suicide.
Draws are not possible.