A plotline might be that Stiles got secretly married while on a trip away from his friends. When he returns, he has to figure out how to integrate his new married life into his old friendships. There could be comical moments like trying to hide his wedding ring or coming up with excuses for why he can't hang out at certain times. Also, the relationship within the marriage could be explored. Is it a marriage of convenience that slowly turns into love? Or was it a passionate love - at - first - sight kind of marriage that they now have to deal with in secret.
A possible plotline is that Hermione secretly marries a character who has a dark past. Maybe he was once involved with the Death Eaters but has reformed. They keep their marriage a secret because they know the wizarding community won't easily accept it. Hermione, being the strong - willed character she is, believes in his change and is willing to take the risk. In other fanfictions, Hermione might marry a character who is not from Hogwarts, like someone from Beauxbatons. They keep it a secret because of the potential rivalry between the two schools.
It could be Lydia. They have a long - standing relationship in the show, and a secret marriage between them would be quite a shock. Maybe they eloped in a moment of passion and are now trying to figure out how to break the news to their friends.
One possible plotline could be that they discover they have more in common than they thought. Maybe they start working together on a project in the wizarding world, like researching a long - forgotten magic. As they spend time together, they realize their feelings for each other have changed from hatred to love. To avoid the chaos that would ensue from their families and friends' reactions, they decide to marry secretly. Another idea is that they are forced into a situation where they have to pretend to be married for some magical reason, like protecting a powerful spell or object. During this time, they start to really fall for each other and end up making it a real, secret marriage.
One plotline could be that they got married secretly to protect each other. Maybe Snape has some dangerous enemies and Hermione wants to help him, so they tie the knot in secret. Another could be that they fell in love while working on a very complex magical project together and decided to marry without anyone knowing because they feared the reaction of others.
Well, it could be that Stiles is secretly a girl and in the fanfiction, this secret is slowly revealed as he falls in love with someone. And the person he loves starts to notice little things that don't quite add up with his supposed male identity, like his more delicate features or his different style of communication.
One possible plotline could be that Natsu has been secretly married to a character from his past. Maybe it was a rushed decision during a dangerous adventure, and they kept it a secret to protect each other. As the story unfolds, his friends start to suspect something is different about him. He becomes more cautious and less reckless, which is out of character for him.
One possible plotline could be that they got married to form an alliance between two powerful factions secretly. Another could be that they fell in love while on a secret mission together that no one else knew about. Maybe Itachi was on a mission to protect Naruto from afar and they developed feelings over time.
His best friend could discover it. Since they are so close, they might notice something different about Stiles that makes them suspect he's actually a girl.
Sometimes, in these fanfictions, Dean is secretly married to a supernatural being. For example, he might be married to a fallen angel. This creates a whole new set of problems as he has to deal with the politics and power struggles within the supernatural world while keeping his marriage a secret from Sam and the rest of the hunting community. It can also lead to some interesting character development as Dean has to navigate his feelings for this other - worldly being and his loyalty to his family.
Well, perhaps a plotline where Luffy and Robin accidentally get trapped in a magical or mysterious place. While trying to find a way out, they grow closer and their hidden feelings start to surface. They have to rely on each other more than ever, and they share secrets and dreams that they haven't told anyone else in the crew. But when they finally get out, they have to go back to keeping their relationship a secret because they are not sure how the crew will react. There could also be a sub - plot where other characters start to suspect something but can't quite put their finger on it.