The idea of the heroes and villains having connections to mythical creatures is also common. Maybe a villain has a power related to a dark, mythical entity, and the heroes have to figure out how to combat it. Additionally, the concept of a mythical creature - filled alternate dimension that somehow intersects with the My Hero Academia world is a theme that many fanfictions explore.
One popular theme is alternate universes. Writers like to explore what would happen if the characters were in different situations, like if All Might was a villain instead of a hero. It gives a whole new perspective on the characters and their relationships.
You can try fanfiction platforms like Archive of Our Own (AO3). There are a large number of 'My Hero Academia Mythical Creatures' fanfictions there. Just use the search function and type in relevant keywords to find what you like.
Some popular themes in My Hero Academia fanfiction include the power of mentorship. We see this in the series with All Might and Izuku, and fanfictions often explore different mentor - mentee relationships. Another theme is the exploration of the darker side of the hero society, like the corruption that might exist. And of course, the theme of self - discovery, where characters find out new things about their quirks and themselves as they face various challenges.
A common theme could be romantic relationships between characters that are not the main focus in the official story. For instance, relationships between characters from different hero classes. Additionally, some fanfictions might explore the idea of a post - apocalyptic My Hero Academia world and how the characters would survive and adapt.
Often, the theme of anticipation and preparation for the new life is common. This includes things like setting up a nursery in the hero's lair or apartment. There's also the theme of how the pregnancy affects the character's powers. Maybe they become stronger or have to learn to control their powers differently while pregnant.
One popular theme is the power combination. Since Gwenom has unique powers and in the 'My Hero Academia' world, there are all kinds of quirks. Writers often explore how these powers could interact or be combined in interesting ways.
One popular theme is her role in the hero academy. It could be about how she navigates the challenges of school life and training.
One popular trope is the 'Quirkless Hero' where a character without a quirk manages to become a hero through sheer determination and intelligence. Another is 'Villain Redemption', where a villain decides to change their ways. 'Time Travel' is also quite common, with characters going back in time to fix things in the My Hero Academia universe.
One popular theme is exploring Stain's ideology further. Many fanfictions dig deeper into his beliefs about true heroes and villains, and how that might play out in different scenarios.
One popular theme is power corruption. All For One's insatiable thirst for power can be explored in this context. Another theme could be redemption, although it's quite a stretch for a character like him. But imagining a scenario where he has a change of heart could be interesting.