Mizuumi no Youkai
湖の妖怪
The Lake Monster was an ancient monster who appeared in episode 040. Although she was not a true youma, she is often considered to be one due to Endymion's attempt to use her in a way similar to the Dark Kingdom youma. She came from the lake near the Steamy Hot Springs Inn. (Source: The Oracle :: BSSM Encyclopaedia)
