Hisshi

In shogi, hisshi or brinkmate (必至 "desperation, inevitability" or 必死 "sure kill") is the situation in which an unavoidable checkmate sequence (詰め tsume) will be created by the player's next move.

Hisshi differs from the situation in which a checkmate sequence is only being threatened to be created in the next move but is still avoidable if the opponent defends correctly. This situation is known as 詰めろ tsumero or threatmate. Thus, hisshi is an indefensible tsumero.

The only way to defend against a loss from hisshi is for a player to not give their opponent a chance to actually create the tsume checkmate sequence and instead initiate their own tsume (with constant checks) before their opponent's move. (Thus, a good exemplification of the saying the best defense is a good offense.)

Although the terms brinkmate and threatmate were coined to translate the Japanese terms, the concepts can equally be applied to western chess and other chess-like games. (See: §Western chess below.)

Figure 1 shows a classic hisshi problem. 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 7d square (Fig. 2).

From this position, Black is threatening to drop their gold to 8c in their next move to render an immediate mate.

Even if White were to try to remove Black's promoted silver with ...Px7d (Fig. 3), this does nothing to prevent the simple mate in one with with G*8c (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 8c square by dropping a defender (such as a gold) to 8b (Fig. 5), then Black can initiate a 3-move mating sequence starting from G*8c (Fig. 6).

Subsequent moves are ...Gx8c, +Sx8c (tsumi).

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

Subsequent moves are ...K-7a, G*7b (tsumi).

Alternately, instead of +S-8c, Black could move P-8c+, then K-7a, G*7b (tsumi).

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 8b square, White can defend against this by dropping a gold to 7a defending the 8b square. With this move, White has removed the threat of Black's tsumero. If Black dropped their gold to 8b now, then White would simply capture it and attack Black's other gold (that is, ...G*7a, G*8b Gx8b).

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