It's great to see progress in editing this game. Good luck with your sprite tool. Based on what I saw in YY-CHR, it can't be straight forward. It displayed tiles side by side, and two tiles needed to be on top of the next 3 tiles..... yeah, can't be fun.
Besides the packing format, this might also be applied to Blue Rescue Team, which appears similar in YY-CHR. (Not to rush you or anything. I know this isn't easy.)
Now that I mentioned Blue Rescue Team, here's VB code to unpack the sbin files. Not that it's really related to the topic, but it's better than sitting there in the deep dark depths of my hard drive.