In novels, the Prince of Demons usually did not directly PK the Princess because the Princess was usually a character in a novel or anime that represented a specific country or power, while the Prince of Demons was another character that represented a different power or goal.
In some novels or anime, there might be a battle between a demon prince and a princess, but it was usually because of a conflict of interest or goals between the two parties, not because the princess herself had evil characteristics. Therefore, the plot of the Demon Prince vs. Princess might appear in specific novels or anime.
The Ice King could be an antagonist. He might be jealous of their relationship and the new baby. He could try to kidnap the baby to have someone to care for him. Another potential antagonist could be some of the more traditional Candy People who don't approve of Marceline being with Princess Bubblegum and having a baby together. They might try to separate the family.
Well, it could be about Finn and Princess Bubblegum going on an adventure in a lemon - themed land. Maybe they have to solve the mystery of why the lemon trees are dying and in the process, they discover new feelings for each other.
For Princess Bubblegum, the kiss might make her more open - minded and less bound by the strict rules she has set for herself in ruling the Candy Kingdom. She could start to incorporate more of Marceline's free - spirited nature into her leadership style. For Marceline, she might become more protective of Princess Bubblegum and the Candy Kingdom as a whole, seeing it as an extension of her love for Bubblegum.
There's a fanfic called 'Candy and Rock'. In this story, Princess Bubblegum and Marceline go on an adventure together. It shows how their different personalities, with Bubblegum's scientific and organized side and Marceline's carefree and edgy side, complement each other. And then there's 'The Moonlit Meeting', which focuses on a more emotional side of their relationship, especially during a full moon in the Land of Ooo.
Well, one of the popular themes is love. Their relationship has romantic undertones in the show, and in fanfiction, it's often explored more deeply. There's also the theme of power. Princess Bubblegum with her scientific and ruling power, and Marceline with her vampire powers can have stories where they deal with power imbalances or combine their powers for a common good. And of course, there's the theme of redemption. If there were past wrongs in their relationship, fanfictions might explore how they can redeem themselves in each other's eyes.
You can try looking on fanfic - specific websites like Archive of Our Own or FanFiction.net. Just search for 'Finn x Princess Bubblegum lemon' on their search bars.
Perhaps in a post - apocalyptic scenario where they are the only two left to defend their land. In the heat of a battle against a powerful enemy, they find strength in each other. Their shared victory is followed by a moment of intense emotion, resulting in a kiss. This could be the turning point where they not only become a couple but also the symbol of hope for the remaining survivors.
Tumblr is another place to look. There are many blogs dedicated to Adventure Time fan content, and some of them might post or recommend Princess Bubblegum x Marceline fanfics. Additionally, some smaller, more niche fanfic communities related to Adventure Time could also be a source. You can find these by searching on Google for 'Adventure Time fanfic communities' and then exploring for the specific pairing.
One idea could be that the baby has unique powers that combine Princess Bubblegum's scientific knowledge and Marceline's vampiric abilities. For example, the baby might be able to control both candy elements and shadows. Another plot could involve the two moms trying to raise the baby in a world that doesn't fully accept their relationship, so they have to face challenges together to protect their family.