Update on Thursday.
Interestingly despite all white UN gods being male and YIS gods being female (apart from the Master of Ethics), humans/percievers are both male and female, despite being black souls of YIS. I wonder if humans are the only ones with biological sex in this universe with Angeks, Devils, and Servants technically having none.
Apparently an angel's number is their number of incarnations or times they have died. So Micheal has only died once as a Prime angel, when killed by Zoss, the ruling king.
Since humans/perceivers are the only ones who can die permanently, I wonder how the reincarnation of everyone else works? Maybe their soul has to hang around in the void (the big white area) until they gain enough power to reincarnate a new body. Micheal seems to have been the only Prime to have returned though, so perhaps it is random the length incarnation?
The other thought I had was that reincarnation occasionally wipes the memories of the soul, meaning a completely brand new identity - thus Michael is the only remaining Prime angel because all the other angels eventually reset their souls while reincarnating.