User blog comment:Saikou The Lewd King/Ancestry Tree/@comment-36674939-20180913051634

Narwhal girls are actually closer to mermaids and lamias according to what she says in-game.

''I am also called a Sea Serpent. In addition to mermaid, I also have the attributes of a sea snake.''

Exactly where they'd fit I can't say for sure, but they are definitely not related to beasts.

Also, "demon" and "yoma" are effectively the same thing under different names that TTR uses rather interchangeably. A lot of ancient monsters (Sphinx, Yamata no Orochi) are part-Yoma, leading me to believe Yoma is effectively a designation for those monsters that haven't strayed far from the bloodline of the Dark God, or in the case of monsters like the Devil Fighter, are pure-blooded demons whose evolution has experienced very little divergence.