Eminence kingdom is a island in the multiverse sea. it is a grass lay out and has a coliseum in the centre.
NPCS:
set spawn npc
Set spawn NPC is there just like with every other island he will set your spawn point there so if you leave and head back to the multiverse sea it will spawn you there.
I don't know the name of the other npc but I know that if you talk to him, he will give you the shadow Eminence, the sword requires 3 sword fragments obtained from the dungeon.
The dungeon is hard as you have a boss with 500,000,000 health so it is recommended to use a high strong aoe fruit like g5.
(I could not find images of the map so feel free to add them if you can.)