Heya! While working on the AU I'd like to share more lore!
-Humans know yokai existed, but believe them to be extinct. In human eyes, yokai were powerful monsters who were chased away by ancient humans. This is mainly here to give more reason to Draxums own backstory as he eventually plays a major role in the AU. According to the Rise Wiki humans drove yokai underground. (Expect Undertale references lmao)
-There are multiple hidden cities across the world. Powerful yokai can teleport to different cities. Weaker yokai need the help of public portals, airships, boats, and carriages.
-Weak yokai, or yokai without a cloaking broach physically can not leave a hidden city. This is due to mystic powers from ancient humans preventing them from leaving. The only bypasses are being incredibly powerful such as Draxum, or having a cloaking broach. As such cloaking broaches are a rare and expensive item. Additionally, if their broach is stolen they can't renter a hidden city.
-The humans turned into mutants by Draxum have significantly higher strength/are more durable/live longer. However, they also suffer from the fact the greatest flaw becomes escalated. I.E: Meat Sweats became much crueler, Mantis became much more greedy, and Warren became much more egotistical.
-Some yokai straight up don't think humans are real/the surface world is fiction much like how humans think yokai are extinct. Many yokai treat humans like we treat Santa or the tooth fairy.
-The battle nexus has expanded lore, I don't want to get to much into it for spoiler reasons but there is a reason for it's existence!