The plot of such a fanfiction could be really interesting. Harry might be in Vegas for some kind of international wizard - Muggle relations mission. While there, he gets caught up in the Vegas lifestyle. He meets a person who is either a wizard from a different culture he's not familiar with or a Muggle with a strange connection to magic. They get married in Vegas, and then the story could explore how their different worlds collide. For example, if it's a Muggle, how does Harry introduce her to magic? And if it's a wizard, how do they handle the cultural differences between their magical upbringings? There could be a lot of humor and drama as they navigate their new relationship and the secrecy that might be required in the wizarding world.
Well, in a 'Harry Potter Marries in Vegas' fanfiction, it could start with Harry being frustrated with the wizarding world's formalities regarding relationships. He goes to Vegas for a break and gets drunk. There, he meets a girl who seems to understand his struggles. They have a wild night and end up at a wedding chapel. After the marriage, he has to figure out how to incorporate her into his life in Hogwarts or wherever he is living at that time. Maybe she has some magical abilities he doesn't know about at first.
He could marry a Muggle he meets by chance in Vegas. Maybe a singer or a waitress who has a big heart and an open mind towards the strange things Harry might do or say because of his wizarding background.
In some versions of this fanfiction, the Vegas part could be a parallel dimension that Harry accidentally stumbles into. There, he discovers a different set of rules and meets a person who is his soulmate in that dimension. Since he has always been a bit of a rule - breaker and a hero, he decides to marry this person despite the differences. It could also be that the story is a comical take on Harry's life, where he goes to Vegas with Ron and Hermione for a lark, and things go hilariously wrong and right, resulting in him getting married.
Perhaps in this 'Harry Potter in Vegas' fanfiction, Harry accidentally apparates to Vegas instead of his intended destination. There he meets a group of American wizards who are using Muggle Vegas as a cover for a secret magic convention. Harry gets involved in a mystery where a powerful magical artifact has gone missing and he has to find it before it falls into the wrong hands.
Well, it could be about Harry and his friends going to Vegas during a break. Maybe they get involved in a magical challenge there, like a wizarding duel tournament with a Vegas - style twist, with big magical prizes and flashy spells.
A 'Harry Potter marries Supergirl' fanfiction might start with Supergirl accidentally landing in the wizarding world. Harry Potter, being the curious and brave wizard he is, approaches her. At first, there are misunderstandings due to their different cultures and powers. But as they start to communicate and learn about each other's worlds, they realize they have a lot in common. They both fight for the good of their respective worlds. This mutual understanding leads to a deep friendship and later, love. Their marriage would be a grand event, attended by wizards, witches, superheroes, and supervillains (the ones who are allowed to come under a truce). It would symbolize the coming together of two very different yet equally amazing fictional universes.
One possible plot could be that after the war, Harry realizes his deep connection with Tonks as they both have lost loved ones and are trying to rebuild their lives. They start to spend more time together, and gradually their friendship turns into love. Eventually, they get married and face the challenges of the post - war wizarding world together.
One possibility could be that in an alternate magical universe, Harry Potter, after all his adventures at Hogwarts and defeating Voldemort, travels to a different realm where he meets a queen. Maybe the queen is facing some magical threats in her kingdom and Harry, with his powerful magic, offers to help. As they work together, they fall in love and decide to get married. Their union could then bring about a new era of peace and cooperation between the wizarding world and the queen's non - magical kingdom.
In the 'Harry Potter marries Blackfire' fanfiction, it could start with Harry being sent on a diplomatic mission to Blackfire's homeland. There, he meets her and is immediately drawn to her strength and intelligence. Blackfire, on the other hand, is initially skeptical of Harry but soon sees his true character. As they work together on some magical problem or task in her land, their relationship grows. Their marriage could then be a symbol of unity between the Hogwarts - associated wizarding world and Blackfire's people. It would also bring about changes in how wizards view different cultures and relationships, as Harry and Blackfire would strive to bridge the gaps between their two worlds.
Perhaps there's a prophecy that involves both of them. They are forced to work together to figure out what it means. Along the way, they discover they have a deep connection, not just because of the prophecy but also because of their shared values of courage and loyalty. This connection eventually leads to marriage.
In the fanfiction, it could start with Harry feeling a strange pull towards an ancient magic site. There he meets Hecate. Hecate is intrigued by Harry's unique magic, which has survived so many dark encounters. They begin to collaborate on magical research, and during this process, their relationship deepens into love. Their marriage unites the Hogwarts magic that Harry grew up with and the primordial magic of Hecate. This causes a stir in the wizarding world as many are both excited and fearful of the new power dynamics that will surely follow.