I want to help you, but... because of the game still in Japanese version, I will not play it.. Try search for a solution at www.gamefaq.com ;D.
Winter dungeon so i assume its a ice dungeon... Try using some fire spell... Because i remember RF 1 i have to use fire spell to get over some dungeon...
you need to get the active seed haslider the lotus leaf then ride it to float on water you can buy it at sia's store