@DW047
Spoiler!
Iirc, the one who resides inside that meteor sword guy is the Blood demon and he's stronger or on par with MC's father. He wasn't completely sealed away by Elder Shin back then they just sealed/took his powers away from him and that powers created both Cheonma, Seol-Ah and the dancer making them sisters. And if he consume the three of them he'll get his full power back. He knows about the regression too but he didn't know who regressed and he didn't retain his memories from his past life.
I don't care about your taste!