You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of Mahoutsukai no Yome crossovers. Just search for 'Mahoutsukai no Yome crossover' in the search bar, and you'll get a list of relevant stories.
A crossover with 'Harry Potter' is also quite common. Imagine Chise going to Hogwarts and learning about a different kind of magic. She could share her knowledge of fae and magical creatures from her own world, and there could be some really cool interactions between the characters from both universes.
There are also other characters like Ruth who can be popular in fanfiction. Ruth's loyalty to Chise can be further explored. Maybe there are stories where he has to make difficult choices between protecting Chise and following the rules of the magical world, which makes for an interesting read.
There could be many. For example, some might focus on the further adventures of Chise and Elias in different magical realms not shown in the original work. It could also explore the backstories of other minor characters in more depth, like how they came to be part of the magical world.
The important characters in 'mahoutsukai no yome light novel' are, first and foremost, Chise. She's the main character around whom the story revolves. Her backstory of being an outcast and her journey to find a place in the magical world are key aspects of the story. Elias, the mage who becomes her husband, is another important figure. He has his own mysteries and his relationship with Chise is complex. And then there's Angelica, who is a friend to Chise and plays an important role in the magical community that Chise becomes a part of.
One of the main themes is the relationship between the two main characters. Their bond, which is complex and evolving, is a central aspect. Another theme could be the exploration of the magical world in which they live, with its own rules and mysteries.
Perhaps the fanfiction could explore the emotional side of Chise's pregnancy. She might have fears and insecurities about becoming a mother, especially given her own difficult past. And Elias, being a non - human entity, might struggle to fully understand her emotions but tries his best to support her throughout the pregnancy.
There could be those in the magical community who see it as an opportunity to study a new form of magic that might be associated with this special pregnancy. However, there could also be more conservative members who are worried about the implications of such a union and pregnancy on the balance of the magical world.
One special aspect could be its unique story setting. It might have a distinct magical world filled with interesting characters and their relationships. For example, the characters' growth and development throughout the story can be very engaging.
One could consider 'The Rising of the Shield Hero' as a similar work. It has a main character in a fantasy world with unique abilities and has to face various adversities. Just like in 'mahoutsukai no yome hoshi matsu hito light novel', there are elements of character growth, relationships, and a world full of magic and mystery. There are also political and social aspects in both that add depth to the story.