Renju VCF #4996428 (5-move VCF)
To move: Black — find the move that forces a win by fours
Winning line
J8 → I8 → J6 → J7 → I5 → K7 → J4 → K3
Why this move works
The answer is J8. You drive White with forcing fours across a five-move VCF (J8→I8→J6→J7→I5→K7).
The decisive J4 makes two winning points at once; White cannot cover both, and K3 makes five. The key is never to let the chain of fours break.