Yuki's Velvet Move: a quiet move puzzle

Black to move. Find the one move that wins. About 1450 ELO.

From a real ChessLvl game against Yuki Tanaka (LVL 1). Black to move: one move wins.

Hint

No check, no capture: the best move is a quiet one that creates an unstoppable threat.

What is a quiet move?

No check, no capture: a calm move that creates a threat your opponent can't meet.

How to spot it

When no forcing move works, look for a move that threatens two things at once.

Tip

Strong players look past checks and captures. A quiet move that threatens two things can be deadlier than either.

Solve it on the board above, or take a hint. Every ChessLvl puzzle is checked by a chess engine to have exactly one best move.