Oh, Eris is an angel alright... an angel of death. She's the one who takes people to the other side; however, this is a lot harder than it sounds. Lottie helps by luring people in and keeping them calm while Eris sends them off.
The two end up falling in love, and the tragic ending is when it's finally Lottie's turn to go (plot twist: Lottie did so well that she's granted the angel of life)