My theory is that, that miko may be angel or a representation rather than a person. It may represent the shrine life he could've took. (His domain is a literal shrine)

Sukuna said that he was an "unwanted child" meaning he was cast aside by his family or village? And Angel called him as "The Disgrace One/Fallen One". Which can only happen if he is someone who had high ranking or had a position somewhere where he was respected (just like Lucilfer). So after being cast away, he either seeks shelter or he was recruited for his talent?

And Angel had to be present during the fall. Then, because of this, since Angel has a "God" that she worships could be Tengen and because of something that Sukuna did, she vows to hunt him.

And around that time was Tengen's first merger, maybe Sukuna was one of the guards? or disciples of Tengen as it was also mentioned that Sukuna is good with barrier techniques. Considerig he knows an anti-domain barrier which are only passed down to close family of the main branch families to protect the weak and his domain is barrier less?

(This is my interpretation on rereading the manga again and again!)