The ori ML, ori FL, FL, and MC are the same people in every world, they were originally from a higher realm. Though that doesn't mean their characters would always be the same, only MC's character is the same, but her character is a bit bland, indifferent to everyone else and indulgent towards the FL, the rest were heavily influenced by the world they were born in.

The ori ML and ori FL doesn't always love each other in every world, sometimes they hate each other too so that's pretty refreshing since each world won't be about similar characters all the time. Sometimes the ori FL is evil, sometimes she's good. But the ori ML is pure scumbag in every world.

The FL too has different personality in every world in the first few arcs but her main personality trait would always be there like her possessiveness for the MC. MC is very OP but never used much of her abilities because she wanted the FL to grow and shine, not be kept under her wings.

The MC sealed her own memories and feelings after each world and the only way for her feelings to be unsealed is by having the FL confess to her. In one of the worlds, the FL was very arrogant and prideful so she wouldn't confess to MC, it was hilarious seeing how desperate she was trying to make MC confess to her while the MC was just staring at her with a confused expression 🤣, she finally submitted in the end and confessed to the MC, only then the MC finally understand her feeling for the FL.

The ori FL originally had someone she liked in the higher realm but that person was killed by the ori ML and had her soul scattered into the small worlds, not sure if the ori FL followed the ori ML into the small world because of him or she did it to find that person's soul since the MTL wasn't clear. You can see in some arcs that the ori FL would sometimes end up with someone else, sometimes men or women, those are that person's soul fragments.