A major theme is the struggle against overwhelming expectations. Izuku has high expectations from himself and others in the world of the story. When he fails to meet them, it leads to his depression. Also, the theme of lost hope is common. He might lose faith in his dreams and his ability to become a hero. In some fanfictions, his depression is also linked to past traumas, like being bullied for not having a quirk initially.
There is a fanfiction called 'Lost in the Abyss'. In this story, Izuku is dealing with depression due to his failures and the expectations placed on him. It's a very emotional read as it shows his journey from a state of hopelessness to slowly finding a glimmer of hope. Another one is 'Tears in the Rain' where his depression is exacerbated by the isolation he feels, and it's really engaging to see how he tries to break free from it.
They may depict him having internal monologues full of self - loathing. For instance, he could constantly think that he's a failure or that everyone would be better off without him. His eating habits might change too. He could either lose his appetite and start skipping meals, or overeat as a form of comfort. In battle, his performance might decline as he lacks the usual drive and confidence, and is more likely to make mistakes.
A frequent theme is his relationship with All Might. In some fanfictions, he might feel that he has let All Might down. All Might's high expectations of him could weigh heavily on Izuku, making him feel like he can't live up to them. This could lead to a downward spiral of depression. Also, the theme of hero society's pressure on him is common. The expectation to always be strong and save others can be overwhelming, and in these fanfictions, Izuku might crack under that pressure.
He would likely be more confident. Having the powers of the Human Torch gives him a new level of strength. So he might stand up straighter and be more assertive in his actions.
One possible reason for Sasuke being depicted as depressed in fanfiction could be his traumatic past. He witnessed the massacre of his clan at a young age, which surely left deep emotional scars. In fanfiction, authors might explore how these past events continuously haunt him, leading to his depressive state. They could show his internal struggle between revenge and finding a new purpose in life.
His friends like Ochaco could help. She might use her zero - gravity ability to assist in handling heavy parts during the construction. Also, Iida could be there to keep things organized and on schedule with his strict sense of order.
It can make them feel less alone. When someone reads about a character with similar feelings in 'depressed reader fanfiction', they realize that others might be going through the same thing.
Fanfiction often takes liberties with the relationship between Izuku and Toga. It could also involve them teaming up against a common enemy. This would require them to put aside their differences and work together. Writers can use this to create exciting action - packed scenes and explore how they would communicate and cooperate in such a situation.
Yes, there are likely fanfictions out there with the concept of 'izuku is loki'. Fanfiction communities are vast and diverse, and many authors like to create crossovers or unique interpretations like this. You can start by looking on popular fanfiction websites such as Archive of Our Own or FanFiction.net.