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The Underworld has a lot of parts. Would be really cool if someone made a map.
>Styx and other rivers leading into it (Consistent lore)
>Big cities (Her debut and early streams), confirmed to have a casino/entertainment district (Hololive Alternative) and likely where her bar is located
>Plains and cliffs giving scenic views into the distance (Red)
>Arid areas leading to Death-Sensei's palace (Christmas Catastrophe)
>Hot springs running over fiery parts, creating secluded areas to relax (Hot Spring ASMR)
>Cold and snowy mountains (Where her dojo is located)
>Areas paralleled by the real world (UnAlive MV, perhaps her own cathedral/castle)
All connected by roads, waterways, and portals- both fixed and where those skilled/authorized can freely teleport.
A bunch of climates and levels, and that's just the stuff directly connected to Mori. There's countless other denizens, and even dangerous beasts (Where she said the spikes on her cape came from)
She just piles on more stuff, usually without thought for consistency, but piecing it all together is fun.