A really interesting plot might be that there's some sort of prophecy in the Supernatural world related to a male pregnancy in their bloodline. Dean unknowingly fulfills this prophecy when he becomes pregnant. John, being the experienced hunter, has to dig deep into old lore to understand what's going to happen. Along the way, they face challenges not only from the supernatural forces that are interested in the baby but also from within their own family. Dean has to deal with the physical and emotional changes, while John has to learn to be more open and protective in a way he's never been before.
One plot idea could be that Dean discovers he's pregnant and is extremely conflicted. He's worried about how John will react, as they have a complex relationship. Maybe at first John is shocked and struggles to accept it, but then realizes he has to be there for Dean. Another idea is that an enemy finds out about Dean's condition and tries to use it against them.
It changes Dean's character significantly. He becomes more in - touch with his emotions. Usually, he's all about the hunt and being tough. But with the mpreg, he has to deal with the hormonal changes and the fear of the unknown related to birth. He might become more nurturing, which is a big shift from his normal hunter self.
Their relationship would likely become more complex. John would probably feel a stronger sense of protectiveness towards Dean. He might also feel guilty for not being able to prevent whatever caused the mpreg. Dean, on the other hand, might become more dependent on John in some ways, which is a big change from their usual dynamic.
The common themes usually revolve around the shock value at first. It's not something you'd expect in the 'Supernatural' world. Then there's the theme of vulnerability. Dean, who is typically portrayed as strong and fearless, becomes vulnerable during pregnancy and birth. This can lead to themes of self - discovery for him. For John, it can be about his role as a father in this unexpected situation. There may also be themes related to the mystery of how this mpreg even occurred in the first place, whether it's some kind of magic or a curse, and how they deal with the implications of it for the 'Supernatural' world they live in.
Well, perhaps the baby is a key to closing a major portal to the underworld. Dean discovers this and has to raise the baby while also preparing it for this great task. Along the way, he gets help from Sam and other friends. They face various challenges from demons who want to stop the baby from fulfilling its destiny.
In some fanfictions, Dean might raise angels with a special purpose. Like he raises a group of angels to help him save Sam who has been trapped in a different dimension or something equally dire. The angels have their own motives and secrets, and as they work with Dean, all these secrets start to unfold, leading to a complex and engaging story.
Another theme could be the danger and mystery that often surrounds the supernatural elements in the show, but now in the context of Dean's pregnancy. For example, there could be a plot where the cause of the mpreg is some sort of dark magic or a new, unknown entity, and Dean and the gang have to figure out how to deal with it while also ensuring the safety of the unborn child. This adds an extra layer of drama and adventure to the story.
One common theme is the exploration of Dean's character in a new and unexpected situation. The mpreg aspect forces him to face emotions and challenges he may not have otherwise.
Another place to check could be Fanfiction.net. However, the tagging system there might not be as precise as AO3. But it still has a decent number of 'Supernatural' fanfics. You may need to do a bit more sifting through the search results to find the really good Dean mpreg stories. Look for ones with high ratings and positive reviews from other readers.
In Supernatural fanfiction, a scenario where Dean is clothed and gagged can be used for various storytelling purposes. It could be part of a capture or hostage - like situation created by an antagonist. Maybe a powerful demon has captured him to prevent him from interfering in their evil plans. Writers might use this to build tension and show Dean's vulnerability despite his tough - guy image.
In some fanfictions, Dean being tape - gagged might lead to some character development. He could learn to communicate in other ways, like using his eyes or body language more effectively. This would make him more resourceful and add depth to his character. For instance, he might be able to signal Sam about a hidden weapon or a way to escape just by using his expressions.