One common theme is friendship. Fatgum is often depicted as a very friendly and approachable character, so fanfics tend to explore his relationships with other characters in terms of friendship. Another theme is mentorship, as he is a mentor in the BNHA world.
One popular 'bnha fatgum fanfic' is 'Fatgum's Big Heart'. It focuses on Fatgum's journey of mentoring a young hero. Another great one is 'The World Through Fatgum's Eyes' which gives a unique perspective on the BNHA universe from his point of view.
One possible analysis could be that their relationship in fanfic often showcases a strong bond of friendship. Bakugo's explosive personality and Kirishima's more stable and friendly nature create an interesting dynamic. Fanfic writers may explore how they support each other during battles or in their daily lives at school. For example, Kirishima might be the one to calm Bakugo down when he gets too riled up, and Bakugo could inspire Kirishima to be more confident in his abilities.
Kirishima is still alive in the manga. The story doesn't have that plot point. Usually, character deaths are significant events and are clearly shown if they occur.
Kirishima is from a manga/anime. His back story involves him having a sense of self - doubt initially. He admired those with strong and manly qualities. He worked hard to overcome his insecurities and develop his own strength and courage, eventually becoming a reliable hero - in - training.
One common theme is friendship. Since they are classmates in the My Hero Academia universe, many fanfics explore how their relationship grows from just schoolmates to really good friends. Another theme is mutual growth. For example, Bakugou's hot - headedness can be tempered by Kirishima's more level - headed nature, and Kirishima can learn to be more assertive from Bakugou. Teamwork is also a frequent theme as they often work together in the story, whether it's in training or in actual hero missions.