Don't tell me...
Seong-ah (the girl idol one) used to be the doppelganger who killed our seong-ah??
main character has memories of a past life.
mom looks just like the idol (who was banging on the car door)
most likely he was her brother that passed after an accident of smth.
it would also explain his timid & small stature as a soul (when being chosen to be a doppel. because he was literally a younger soul when he passed)
they probably share a last name that he cant remember but his brain is telling him its Seong
I'm excited but also scared, I feels like it's gonna be sad ending?? like sweet sad tragedy ending uh