Shop 10
First, if you don't use the Bee Jayro to reach Rasetsu's castle you shouldn't have any problem. If you used the Bee Jayro, you have to escape from the battle (Put the cursor on a character that hasn't been moved (blue) yet and press enter) and fight this battle:
This is a Chaos battle, but there's a shop here and you'll find the useful Chrome fist
CREDIT:
