I'm late to the discussion but whatever.
I have a feeling that Nanachi's bottom half is just gone, connected to whatever machine/relic is in the bottom part of that bag.
Nanachi made it specifically for Riko, whose entire ethos is continuing the journey in whatever condition she's in.
That being...
I think he's getting skinnier by the day. Compared to his first appearance in his villain costume. Now his ribs is much more prominent when he's donning his costume.
Bro they are literally diving a hellhole where people die a lot, it's daily occurrence. It's been established since early on that cave delving is a profession with insane fatality rate. AND our characters are currently diving uncharted region of said hellhole.
Reading this manga for 60 something...