One possible plot could be that Deku discovers Toga has a family she has been separated from. Deku decides to help her reunite with them. Along the way, they face various villains who are after Toga. As they journey together, they start to understand each other better and form an unexpected bond, not just between them but also with Toga's family when they are finally found.
For Deku, his character can be developed by showing his struggle to understand Toga's family's situation. He has to balance his hero values with the new perspective he gets from being involved with them. For Toga, her character can grow as she learns to trust Deku more in the context of her family. Her family members can be developed by giving them unique personalities and backstories. For example, one family member could be a former hero who retired due to an injury, and this could add depth to the story.
There are very few, if any, truly family - friendly fanfics with such a concept. The idea of a character getting a girl pregnant is often part of more mature or inappropriate storylines. However, some fanfic writers might take this concept and twist it into a more positive and educational story about responsibility and growing up, but these are rare.
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.