A frequent theme is the backstory exploration. Writers often create scenarios where we learn more about their pasts and how those pasts might have led to their current relationship. There can also be themes related to hero training. Maybe they team up to train students in some fanfictions, and we see how their teaching styles blend or clash. Also, some fanfictions explore the idea of them facing a common enemy together and how their bond grows stronger through that experience.
One common theme is friendship. They are colleagues in the My Hero Academia universe, and many fanfictions explore the deepening of their friendship, like how they support each other through tough times at work or in battles.
Some fanfictions also have a mentorship theme. Since Allmight is a very experienced hero, he could potentially be a mentor to Present Mic in certain aspects. This could involve training, or guiding him in making important decisions. And of course, there are some fics that explore a more romantic relationship between them, though this might not be as common as the other themes.
A common theme is their shared work environment. Since they both are part of the U.A. High School faculty, many fanfictions explore how they deal with the daily chaos of teaching and protecting the students. Another theme could be their contrasting personalities. Nezu is very intelligent and calm, while Present Mic is more energetic and outgoing. Fanfictions often play with how these different personalities interact and complement each other.
Love and support is also a big theme. Some fics take their relationship to a romantic level, showing how they love and support each other through thick and thin. They might comfort each other after a tough battle or just be there for each other during a bad day.
Some fanfictions also explore the idea of a romantic relationship between them. They might show how their friendship could potentially develop into love over time, with themes like hidden feelings and the discovery of new emotions for each other.
One more theme is the exploration of their quirks together. Present Mic's sound - based quirk and Eraserhead's erasing quirk can be combined in really creative ways in fanfics. Writers often use this to create unique battle scenes or problem - solving situations, which adds an exciting element to the stories.
Well, I'd recommend searching on AO3. It has a great collection. Just type in 'Present Mic x All Might' in the search bar, and it'll show you relevant fanfictions. Some might be sorted by popularity or by the date of update. If you join some My Hero Academia fan groups on social media, like Facebook groups or Discord servers dedicated to the show, you can ask for recommendations from other fans. They might point you to some hidden gems that you wouldn't find easily on your own.
A theme could also be his heroic deeds. Fanfictions could be written about him saving a large group of people from a powerful villain using his sonic powers in creative ways, like creating a sonic shield to protect them or using his voice to confuse the villain into making mistakes.
One common theme is mentorship. All Might is often portrayed as a mentor to the OC, guiding them in their journey to become a hero.
A lot of all might x endeavor fanfictions also touch on the idea of redemption. Endeavor has a rather complex backstory with his family issues, and in some stories, All Might plays a role in his journey towards redemption. They also might explore the theme of mentorship, where either one could potentially mentor the other in different aspects, like All Might teaching Endeavor about public relations as a hero, or Endeavor helping All Might with some combat techniques. There's also the theme of friendship that develops over shared experiences, such as fighting against a common enemy or dealing with the politics within the hero community.