This is me spitballing but seeing as how the 6th LB houses more phantasmal creatures than humans, had its core replaced with rhongomyniad and Beryl's fascination with Mash do you think the reason we haven't seen his servant is that somewhere along the line he turned himself into a demi-servant?
ive considered demiservant beryl yeah. back in fsn already there was a throwaway line about some masters choosing to fuse with their servants so it doesn't even have to be through the animusphere style human experiments. pepe's backstory reveal in lb6 of coming from a kind of cult that intended to find a way to be corrupted into a tengu also lends credence to the idea that beryl's inhumanity is the result of some family line's unethical experimentation and that's why he's drawn to mashu.
i hope they won't go with the servant who beryl summoned as crypter being himself though, because the bond between the crypters and their servants is a massive draw of the lostbelt arc for me. it's suspicious that we haven't seen his servant yet but there could be any number of explanations for that, and my personal bet is on his servant being oberon
