There is a cave located near the Mist Village that is covered by mist so thick, it can even cloud the Byakugan eyes. This cave is actually the shrine to the spirit of Water, Undine. To find your way through the cave, follow the rule on the Summon List. Once you located the altar, you will see that it is actually underwater, surrounded by a circular patch or land. You must call out to Undine and face her in battle. Once you have defeated her, you must make a vow as the summoning contract. If the vow is broken, another may overwrite the contract with their own vow.