One common theme is his growth as a sorcerer. Many fanfics focus on how he hones his skills and becomes stronger. Another theme is his relationships, like his friendship with Yuji or his complex connection with the Zenin family.
There's a fanfic called 'Megumi Fushiguro: A Different Path'. In this, the author takes Megumi on a completely different adventure from the original story line. It's really interesting to see how his character develops in this new scenario. Also, 'Megumi's Hidden Powers' is a fanfic that uncovers some potential powers that Megumi could have, which makes for an exciting read.
The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
Deku might be completely shocked at first. Since Bakugou has always been so aggressive towards him, he would never expect such a confession. He might just stand there, mouth agape, not knowing what to say.
His friends could come to the rescue. Bakugo, for instance, might use his explosive power to break into Toga's hideout. He's always been competitive with Deku, but he also cares about him deeply.
In 'deku meets future deku fanfiction', perhaps the future Deku warns the present one about upcoming threats. He could tell him about villains he'll face in the future and how to defeat them. This would give the present Deku an edge in his battles and also in his growth as a hero.
Well, obviously Deku in two forms - the younger and the older version are the main characters. The younger Deku is the one who is still growing and learning, while the older Deku has more experience.
As of now, Deku is very much alive in the manga. The plot hasn't reached a point where he meets such a fate. Usually, main characters like Deku have significant story arcs and aren't easily killed off.