In the fanfiction, Merlin could propose during a dangerous adventure. They might be facing a great evil, and Merlin realizes that life is too short not to make Freya his. So, in the heat of the moment, right before they're about to battle the foe, he turns to her and says something like 'Freya, if we survive this, I want you to be my wife. I love you more than any magic or power in this world.'
Well, perhaps Merlin would plan an elaborate, magical proposal. He might use his magic to create a beautiful, enchanted garden filled with Freya's favorite flowers and glowing orbs of light. Then, in the center of this magical place, he'd get down on one knee and present her with a ring made from a rare, enchanted gemstone that has special meaning to them both.
She might be completely overjoyed. With tears of happiness in her eyes, she'd immediately say yes and throw her arms around Merlin. After all, she loves him deeply and has probably been waiting for this moment.
Well, it could start with Merlin finding Freya in a difficult situation. Maybe she's being chased by some dark forces. Merlin uses his magic to save her and in that moment of relief and gratitude, they share a kiss. It could be a very tender and innocent kiss, filled with the start of new feelings between them.
A plot could involve Merlin and Freya getting married in secret. Then, as they start their new life together, they discover that Freya has a special connection to a hidden realm. They must work together to protect this realm from dark forces that are trying to invade it. Their married life becomes a series of adventures as they fight side by side, using their combined magic to keep the realm safe.
A plot for a Merlin and Freya pregnancy fanfic could involve a magical pregnancy. Since Merlin has magic and Freya has her own unique abilities, the pregnancy could be anything but ordinary. There could be signs and omens that the baby is destined for something great. They might have to protect the unborn child from dark forces that sense its potential power. The story could show how they work together to keep the baby safe. It could also include some tender moments where they talk to the baby in the womb, sharing their hopes and dreams for its future.
Well, a plot twist might be that Freya discovers she's pregnant with a special kind of magic - not just normal magic but something that is a blend of different magical realms. This causes a stir in the magical community and they have to deal with the politics and jealousy that comes with it. Also, Merlin might have to hide this fact from Arthur for a while as he fears Arthur's reaction to such a strange magical occurrence.
Love is a very common theme. Their relationship, whether it's a budding romance or a deep platonic bond, is often explored. Another theme is magic. Since both are magic - related characters, how their magic interacts or complements each other is frequently written about.
One major theme is sacrifice. Given their circumstances in the show, many fanfictions show either Merlin or Freya sacrificing something for the other. For example, Merlin might sacrifice his safety to protect Freya. Also, the theme of redemption can be found. If Freya was seen as having a 'dark' side in some interpretations, fanfictions may explore her journey of redemption with Merlin by her side. And of course, the theme of adventure is also common as they go on various quests in these fictional stories.
Well, it could be that Ben decides to propose during a big event. For example, during a royal ball where all their friends and family are present. He gets on one knee in front of everyone, and Mal is completely surprised. Maybe there are some misunderstandings before the proposal, like Mal thinking Ben is too busy with his royal duties to think about their relationship at that level, but then he proves her wrong.
Well, perhaps Percy takes Annabeth on a quest to a special location, like an ancient Greek ruin they've always wanted to explore. During this adventure, he finds the perfect moment when they're alone and surrounded by the beauty of the place to pop the question.
Maybe Sasuke has been secretly planning the proposal for a long time. He starts by taking Sakura on a journey to different places they've been to in their past adventures. Along the way, he drops little hints. When they reach a beautiful, secluded spot by a waterfall, he gets down on one knee. He tells Sakura that she is the only one who has truly understood him and that he wants to spend the rest of his life with her. Sakura is shocked but then hugs him tightly and accepts.