Puzzle #Uyjzm: why does 5二金打 not work?

lishogi.org/training/Uyjzm

After 5三金打, Gote's King goes to 6一. Can somebody please explain me how the King can avoid checkmate if I drop 金 on 5二?

This isn't the first puzzle I don't understand. It may be too obvious for strong players, but I can't see it.

1

If you drop 金 on 5二，Gote's King can go to 7二. Then Gote's King can avoid checkmate in a short time.

2

You're right, thanks. Problems with diagonals are common. I wonder if the non-checkered board is the problem. It looks like I couldn’t adapt to the shogi board yet, and still rely on dark and light squares to see all possible diagonal moves.