Perhaps in the fanfiction, Finn and Puck find themselves in an alternate universe where being gay is the norm in the glee club. This allows them to freely explore their relationship without the fear of judgment. They could then face the challenge of how to bring this new - found confidence back to their original world.
One idea could be Finn getting a bad case of the flu right before a big performance. His friends in Glee club would then have to figure out how to cover for him or help him get better in time. Another could be that Finn has an ongoing illness that he's been hiding from the club, and it finally starts to affect his ability to participate fully. Maybe he faints during a rehearsal, and then everyone rallies around him to support him through his sickness.
There could be authors who are known for creating really engaging storylines in this type of fanfiction. They might write about Finn and Puck's relationship evolving over time, through different challenges like family issues or competition within the glee club. These authors are great at building tension and drama in the story.
A really interesting plot could be that their new - found sibling relationship causes a stir in the Glee club. Some members might be skeptical, thinking it's a ploy for more attention. Meanwhile, Rachel and Puck have to deal with the fact that they have different friends in the club. They could have to navigate through the club politics while also getting to know each other as siblings. For example, Puck's bad - boy image might clash with Rachel's more uptight personality at first, but they gradually learn to accept and even complement each other.
A really cool idea for a fanfiction could be that Rachel and Finn swap personalities for a day. Finn suddenly becomes super - focused on his Broadway dreams like Rachel, and Rachel has to deal with Finn's more laid - back attitude towards things. It would be a humorous and also a great way to explore their relationship from a different perspective.
One common theme is redemption. Puck especially has a bit of a rough past in the show, and fanfiction often explores his journey towards redemption, with Finn sometimes playing a role in that. Also, the theme of family comes up. Given their different family situations, fanfiction might look at how they support or envy each other's family situations. There's also the theme of loyalty, as they are part of the Glee club and have to be loyal to their friends there, which includes each other.
One idea could be that Finn has a hidden talent for songwriting that he discovers while in the Glee Club. Another could be that he has to overcome some initial shyness about performing in front of others. Or perhaps he forms a special bond with one of the other members that helps him grow as a person and a performer.
One common theme could be the exploration of unexpected parenthood. Since it's mpreg, it's a very different take on having a child. Another theme might be the relationship between Puck and Finn, how they deal with this new situation together or separately.
One plot idea could be that Rachel and Puck initially panic when they find out about the pregnancy. They might struggle to tell their friends and family, especially considering their different personalities and backgrounds in the Glee club. Maybe they decide to keep it a secret at first, but as the pregnancy progresses, it becomes harder to hide.
One popular glee finn and puck fanfiction is 'The Unlikely Bond'. It explores their friendship in a really interesting way, showing how they support each other through different challenges in the Glee club. Another great one is 'Changing Tides' which delves into their relationship and how they grow as individuals while also being there for one another.
Maybe the arranged marriage is part of a deal to save their families' reputations. Rachel's family wants her to marry into Puck's family to gain some social standing, and vice versa. Initially, Rachel is furious as she has her own plans for stardom. Puck, on the other hand, is more laid - back about it. But when Rachel's Broadway dreams start to crumble, Puck uses his family's connections in the music business to help her, which makes her see him in a new light and begins to accept the arranged marriage.