It depends on the specific situation and the character's personality. Some heroes might have moments of fear but overcome them through their determination and sense of duty.
One common theme is the power - dynamic between them. Since Mirko is a strong and experienced hero and Deku is on his journey to become a great hero, their relationship can explore how they support and learn from each other in terms of power and skills.
There might be a fanfiction where Izuku is training under Mirko. She pushes him to his limits and helps him unlock a new aspect of his quirk. This story could focus on their mentor - mentee relationship and how Izuku grows from it.
There are fanfictions that explore Mirko's backstory in more detail. For example, how she became such a strong and fearless hero. It might delve into her training days, the challenges she faced, and the people who inspired her along the way. In some fanfictions, she could have had a mentor who taught her unique combat techniques that she uses in her battles now.
You can start by looking on websites like Archive of Our Own (AO3). It has a large collection of fanfiction from various fandoms, including ones for Izuku and Mirko. Just search for their names and you'll likely find many interesting stories.
One highlight is his amazing kickboxing career. His left high kick was a feared weapon. Another is his entry into the UFC which brought him international fame. He also had epic battles against top fighters.
Another option is to check out some dedicated My Hero Academia fanfic forums. The fans there are really into sharing their works. Sometimes, they even collaborate on writing. So it's a great place to search for that specific 'mirko x deku fanfic' you're interested in. You can also interact with other fans and ask for recommendations.