That alien in the 2nd to last page looks exactly like one of the shadows from Persona 3/4/5 ( i can't find the exact one, too many shadows to sift through on the wiki)

I looked into it...the shadows in the persona games were actually pulled straight from the Shin-megami tensei games. But in SMT the shadows are specifically demons.... so its stands to reason that the original design for the shadows/Demons for Persona/SMT comes at-least partly from traditional Japanese mythos/folklore (neat!)

so now going back to Dandadan, i'm asking myself why is this demon an alien? Did I smoke too many joints? Is there such thing as too many joints? Probably