Brinkmate

Example

Fig. 1. (pre-)Hisshi problem ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1                   2 王 銀 歩             3 歩 歩               4                   5                   6                   7                   8                   9 ☗ pieces in hand: 金

Fig. 2. Hisshi (answer) ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1                   2 王 歩             3 歩 歩 全             4                   5                   6                   7                   8                   9 ☗ pieces in hand: 金 S-74+

Figure 1 shows a classic hisshi problem.^[1] Here, Black does not have a way to immediately checkmate White's king. However, Black can create hisshi by moving and promoting their silver to the 74 square (Fig. 2).

Fig. 3. White's Response #1: Capture ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1                   2 王               3 歩 歩 歩             4                   5                   6                   7                   8                   9 ☗ pieces in hand: 金 ... Px74

Fig. 4. Tsume #1 (1 move) ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1                   2 王 金               3 歩 歩 歩             4                   5                   6                   7                   8                   9 ☗ pieces in hand: – G*33

From this position, Black is threatening to drop their gold in hand to 83 in their next move to render an immediate mate.

Even if White were to try to remove Black's promoted silver with ...Px74 (Fig. 3), this does nothing to prevent the simple mate in one with G*83 (Fig. 4).

White has two possible ways to attempt to defend against this threat.

But, since this is hisshi and not merely tsumero, all attempts are futile as explained below.

If White tries to defend the 83 square by dropping a defender (such as a gold) to 82 (Fig. 5), then Black can initiate a 3-move mating sequence starting from G*83 (Fig. 6).

Subsequent moves are ...Gx83, +Sx83 (tsumi).

Fig. 7. White's Response #3: Escape ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1   王               2   歩             3 歩 歩 全             4                   5                   6                   7                   8                   9 ☗ pieces in hand: 金 ... K-82

Fig. 8. Tsume #3 (3 moves) ☖ pieces in hand: all the rest 9 8 7 6 5 4 3 2 1   香 桂               1   王               2   全 歩             3 歩 歩             4                   5                   6                   7                   8                   9 ☗ pieces in hand: 金 +S-83

If White's king tries to flee to the 82 square (Fig. 7), then Black can initiate a 3-move mating sequence starting from +S-83 (Fig. 8).

Subsequent moves are ...K-71, G*72 (tsumi).

Alternately, instead of +S-83, Black could move P-83+, then K-71, G*72 (tsumi).

Hisshi vs tsumero

The first adjacent diagram has an example of tsumero that is not hisshi. It is now White's turn to play. Although Black has a possible checkmate in their next move by dropping their gold to the 82 square, White can defend against this by dropping a gold to 71 defending the 82 square. With this move, White has removed the threat of Black's tsumero. If Black dropped their gold to 82 now, then White would simply capture it and attack Black's other gold (that is, ...G*71, G*82 Gx82).

In the second diagram, there is an additional pawn positioned on 73. This difference gives Black hisshi (as well as tsumero). Any defense attempt by White will fail. White's ...G*71 will be met with G*72 Gx72, Px72+ (tsumi). There are similar mate sequences if White tries ...R*32, ...G*82, etc. Similarly, it is impossible for White's king to escape with ...K-71.

Silver on the belly tactic

Silver on the belly (腹銀 haragin "belly-silver") is a basic brinkmate tactic in shogi. This tactic positions a silver (by moving there or by dropping) directly on either side of the opponent's king. The adjacent diagram shows a typical silver on the belly brinkmate. Here the silver is placed on the 82 square. The one-move mates +R-81, +Rx91, S-81=, or Sx91+ are unstoppable. For instance, if White moves P-94, then +Rx91 is mate, and if White moves N*81, then the silver or dragon taking 81 are mates.

That leaves the longest (7-move) mate sequence in which the king attempts a futile escape starting with P-84. Subsequently, the dragon chases. Thus, 2. +Rx91 K-83, 3. +Rx93 K-72, 4. +R-73 K-61, 5. +R-71 is a mate.