DragonKing: Here black (in Japanese style) made "mating net" around white's king, and they king are out of threat. Now black have mate threat: N-5c= mate. If white do move G-4b, then N-5c+ a)Gx5c Rx2b+ Bx2b S*4b mate! b)Gx4c Rx2b+ Bx2b S*5b mate!
You must enoght pieces in hand for mate!