What about Belia? Do you have any ideas and or suspicions?
Spoiler
Belial is the one who's name means worthless. She already seems to know you're a Valla and is the one warning you not to reveal you're a Valla to the goddess. Unless Belial is messing with the protag, you can rule out her as the goddess. Now, it would be possible for her to work for the goddess, if she was looking out for you. I a manner of "I don't want to kill this guy, so let's try to scare him off" sort of way.