One idea could be that the kiss is a moment of realization for both of them. Maybe they've been through a dangerous adventure and in that moment of relief, the kiss just happens. It could be the start of a new chapter in their relationship, where they finally admit their deeper feelings for each other.
Another plot idea is that the kiss is part of a deal. The Doctor has to kiss Rose to save her from some sort of alien threat. But as they kiss, they both feel a real connection that they hadn't expected. This then causes them to re - evaluate their relationship and how much they mean to each other.
One idea could be that they discover the pregnancy in the middle of an adventure. Maybe they're on a planet with some strange energy that affects the Doctor's biology in an unexpected way, leading to the pregnancy. They then have to deal with the challenges of protecting the unborn child while also facing the usual threats in the universe.
Perhaps a plot in 'Doctor Rose Dark Reunion Fanfiction' could involve a reunion that is not as joyous as expected. The Doctor arrives to find Rose in the middle of a conflict with a new, powerful and dark force. She has been trying to hold it off on her own, and now they have to figure out how to stop this force together. Along the way, they might also have to deal with their own feelings that have changed during their time apart.
Another idea is that they are in a time - locked situation where they are cut off from the TARDIS. They must rely on their wits and the help of some new friends they make in that situation to survive during the pregnancy. It could also be a chance for Rose to learn more about the Doctor's past as they wait for help.
One idea could be that Rose returns during the 12th Doctor's time and has to adjust to his new personality. Maybe she teams up with Bill to help the Doctor solve a mystery on a strange planet. They could discover an ancient civilization that has a connection to Rose's past adventures.
One idea could be that in a moment of extreme danger, Merlin and Arthur share a kiss as a way of saying goodbye, not realizing they'll both survive. It could be a spur - of - the - moment, passionate kiss that catches them both by surprise. Later, they have to deal with the newfound feelings this kiss has unearthed.
One plot idea could be that after the kiss, they face opposition from their families. Darcy's family might think Elizabeth is not of a high enough social standing, while Elizabeth's family could have misunderstandings about Darcy's intentions. Another idea is that the kiss is a spur - of - the - moment thing during an argument, and then they have to deal with the emotional fallout and realization of their feelings. Maybe they are in a public place when they kiss, and it causes a scandal in their society, forcing them to either confront or hide their relationship.
Perhaps they kiss in secret at first. Then Renesmee starts to have strange powers emerging because of the strong emotions from their relationship. Jacob is worried about how this will affect Renesmee and tries to find a way to control or understand these new powers. It could lead to a journey of discovery for both of them.
Maybe they are in a foreign location, undercover. The whole undercover act makes them pretend to be a couple and the kissing is part of their cover. But as they kiss, they start to realize that there are real emotions behind it. For example, Riley might notice MacGyver's genuine care for her through the kiss and it makes her see him in a new light.
One idea could be that their kiss is a moment of realization. Maybe they've been enemies or at odds for a long time, and the kiss makes them see each other in a new light. For example, Morgana realizes that Merlin's magic isn't as bad as she thought and that he has been trying to protect Camelot all along. Another plot could involve a magical bond that forms through the kiss. This bond could give them shared powers or make them telepathically linked, leading to some really interesting interactions as they learn to deal with this new connection. A third idea is that the kiss is a secret pact. They kiss to seal a deal to work together against a greater evil that threatens Camelot, but they have to keep their new alliance a secret from everyone else in the kingdom.
One plot idea could be that they finally kiss after a long period of secretly having feelings for each other during a dangerous mission. When they think they might not survive, they confess their love through that kiss.