The creator of the watchmen series
Ever since the chapter that showed the symbols in Canvas Town, I've been thinking that the other symbols actually other items for different series, I believe that all the giants we see are actually the original creators of these series including the Watchmen series, so I believe that in an ancient time these guys were aware of the name god, and in an attempt to reach godhood they make their individual series but instead of becoming gods they lost their sanity and become monsters( similar to Rudo and Mymo's new form) I believe that in an attempt to stop anyone else for finding about God the floating islands were created( which is why the name god doesn’t exist on the lower world, and why jinki doesn’t exist on the sphere), the creator of the watchmen series became the watchman we see on the border and only always people with Watchman series to go past. Anyway back to the other murals, please stick with me cause this might be a reach I think that the one with the eye is something passed down to Corvus and is meant as a way to keep and eye on the lower world threw all the picture of eye we see everywhere, and i think that one of them belongs to the Nijiku family. And the other most Likely Tamsy as he was seen to be some sort of royalty.