In shogi, Side Pawn Capture Bishop-33 (横歩取り3三角 or 横歩取り☖3三角 yokofudori san-san kaku) is a set of variations stemming from the Side Pawn Capture opening, in which White first trades pawns on the eighth file and then blocks Black from trading bishops by moving White's bishop to the 33 square.
White must stop Black's bishop trade to avoid a trap.
(This may be done also by blocking with a knight (N-33) or by White initiating the bishop trade from their side.)
The aerial term refers to the way both players' rooks are positioned above their camps on the middle ranks 4, 5 and 6.
The ☖R-84 opening frequently starts by moving the rook back immediately.
Postponing the rook retreat allows White to wait and see whether Black will next drop a pawn to the 87 square.
As a result of this flexibility, 9...S-22 has become the more common move in professional games compared with 9...R-84 and is, thus, less revealing of White's strategy.
P*87 sequence is shown below with the middle rank rook position in §☖R-85 variation.)
Black has a choice of moving their king straight up to defend the line of pawns broadly as well as moving their king off of the 95–59 diagonal which is susceptible to bishop drop attacks on 95, or moving their king up and leftwards to protect their left gold in case White initiates a bishop trade.
The variation was created by Sasaki as he did his research on his playstyle on the shogi board he inherited from Nobuyuki Ōuchi who died in 2017.
Unlike the Aono variation, when White captures the side pawn with Rx76, Black can move the knight to N-37 regardless of it.
In the Aono variation, following Rx76 White will aim at a bishop exchange with Bx88, which will be followed by Sx88 leaving the left gold unprotected and easily captured by the rook, hence Black needs to play something else before N-37.
This allows the bishop in hand to be dropped to the 77 square attacking White's rook on 86.