Ayu is played on the intersections of an odd-sized square board. At the start of the game, black and white pieces are arranged in an interspersed pattern.

Ayu initial position
  • In these rules, 'adjacent' always means orthogonally adjacent.
  • A unit is a singleton or group. A singleton is a piece with no adjacencies to like-colored pieces. A group is a set of like-colored, adjacent pieces.

Black plays first, then turns alternate. On each turn, players must complete one of the following actions:

  • Move a friendly singleton to an adjacent empty point.
  • Take a piece from a friendly group and place it on a different empty point adjacent to the same group. All stones that were joined in a single group before the move must still be joined after the move.

Every move must reduce the distance between the moved unit and the closest friendly unit. The distance between two units is the shortest path of adjacent empty points between them, i.e. the number of consecutive moves one would need to join them.

If a player can't make a move on his turn, he wins. This usually occurs when said player has joined all his pieces in a single group.

If a board position is repeated with the same player to move, the game will be declared a draw. This is a theoretical possibility if both players cooperate to it. You can find an example of a possible core of such a cooperative cycle in About Ayu. In actual play cooperative cycles do not occur.

Turn order balance
The pie rule can be used in order to balance the game. In that case White will have the option, after (and only after) Black's first move, to change sides instead of making a regular move.

An essential part of the strategy lies in building long walls between enemy units, thus forcing the opponent to spend many more turns connecting them. However, one should be careful not to lock up all enemy units completely, as it might deprive the opponent of all available moves. Also, playing from the outside inwards is more efficient, as it helps you not to leave any units behind.
The distance rule has some interesting tactical implications: sometimes, in order to move a unit (A) in the desired direction, you'll have to first move away the unit (B) which is closest to it so that A isn't “engaged” to B anymore.

Ayu, short for "Attach Your Units", is arguably an essential game of approach moves. The rules have been kept to a minimum so as to let the featured mechanism unfold by itself. The result is a very organic and innovative game with great strategic potential.

The diagram on the left shows the relative distances between every pair of the white units A, B and C. Four moves are needed to join A and B, while C and A are only two moves away from each other. Therefore, if A is moved, it must get closer to C. The next two pictures show the only moves available to that group in its current position. Note that the center piece in it can't be moved, as the group would be left split after the move.

In the diagram on the left, if White plays the marked move, he will lose immediately, as Black will have no moves available on his next turn. Note that this is a legal move, even if the White group is momentarily split during the move.

White can win, instead, by entering the sequence below. In the last diagram Black still must (and can) move, after which White's one unit is immobile.