Arcane sky/mirage sky stand for a crafting ability, u improve it with arcane sky pills fro gods givings
Arcane sky = requirement for first half of skills
Mirage sky = the other half of primals
I, II , III , IV , V .... X stand for roman numbers
They mean 1,2,3....,9,10
Thats leveling
When u reach arcane sky x u unlock mirage at the npc near the army in order to lvl up ur mirage
U need mirage and arcane sky x in order to craft all primals
Morai is a different world in which u farm different skills in 3different orders
Can get in 1st time at elysium village then from calendar or illusion stone