It had been a pretty normal day in the Netherworld when suddenly Flonne found herself in a different world, pulled there by a mysterious gateway in a dystopian city called Veles in Belarus, in the 1950's. It was one of the few human cities left on Earth, which had fallen to a virus, that caused those infected to become undead. (Aka Zombies!)
Luckily she wasn't completely alone. Laharl had been brought there some time ago before her. At first, however, he was wary of her, as the last time he'd seen her she'd still been an angel trainee. Somehow Laharl had not yet experienced the events in Celestia that had turned her into a fallen angel. Eventually Laharl came to accept she really was Flonne.
Then they just did the best they could, surviving on little food and their powers drained by the gate to barely anything.
Every so often the undead world outside would attempt to make it's way into the city and one day an infected cat managed to creep in to the city. Flonne couldn't ignore a sickly animal, but her attempt to help her landed her with a scratch. That's all it took for her to be infected with the virus.
She started getting sick and by the evening was completely bedridden. Laharl went to the clinic for help and she was given a grim diagnosis. With little time to live and the virus painfully through her system, she was given the choice to put an end to it before the infection reached it's cruellest symptoms. So... her suffering was put to an end.
That's all Flonne remembered... clutching Laharl's hand as she closed her eyes. The next thing she knew, she was back in front of the gate, somehow brought back to life. To this day Flonne isn't sure what happened, but she was very, very thankful to be alive.
Since then, Laharl and Flonne were closer than ever. They'd been needing some extra money for a long time, so Flonne started helping at the clinic, putting what small amount of her healing magic to use. People came and vanished, and eventually Flonne had taken over the clinic.
And then Etna appeared. Finally the three of them were together again, though Etna had been brought from another time much like Flonne had, but luckily Laharl was a little more used to the concept.
It was around this time Flonne was starting to feel things for Laharl and had even admitted she liked him, but everything was mostly just awkward. And then one day they had an argument and Flonne accidentally blurted out the big L word. Yeah, that was a shocker for Laharl. At first he seemed to want to change her mind, but eventually it seemed he at least had accepted this was how she felt.
Then came the quiet news amongst those who'd been brought to Veles from other worlds... finally there was a plan to try to take the gate, and when there was a large zombie attack, they acted, and succeeded! And thus they were able to return finally to the Netherworld, finding themselves back at the very moment they'd been taken... which meant while Laharl had to wait for Flonne to remember what had happened, Flonne immediately remembered. Luckily Laharl hadn't messed up what had happened in Celestia to screw up the timeline, and so slowly they settled back into their normal life in the Netherworld. ...Well, as normal as life ever really is there.
(Yinza's write up of this stuff
is better. lol)