This is one of those points where canon is flexible. General consensus seems to be it’s sort of like Twilight but with a demon instead of a vampire- teenage/young adult human girl named Mizar meets ~mysterious guy~ named Al who turns out to be the demon Alcor and they fall in love and shenanigans ensue. And then something about the Woodsman.

I (Mod H) did write a short summary when the Twin Souls name was first used, but canon’s moved on from that, and as long as it’s Mizar x Alcor cheesy romance novel stuff you’re golden.