Typically, these fanfics often focus on their relationship, whether it's friendship or a budding romance. They usually incorporate elements from the original 'My Hero Academia' universe, like their hero training and the challenges they face at school.
One possible motive could be a long - held grudge that has festered over time. Maybe Bakugou's constant bullying in their past finally pushed Deku over the edge. Another could be some sort of mind - control or dark influence that made Deku act out of character.
Bakugou could use his words. He might tell Deku that he believes in him. For example, he could say 'Deku, you may be a nerd but you're a strong nerd.' It's a backhanded compliment but it shows he has faith in Deku.
One common theme is the development of an unexpected friendship. Given their different personalities in the original series, fanfiction often explores how they can bridge the gap and become friends or at least respect each other more.
Often, in 'uraraka x bakugou fanfic', there is a lot of emotional growth. Bakugou might learn to control his temper better because of Uraraka, and Uraraka might become more confident in herself. The fanfic uses their relationship as a vehicle for personal development for both characters.
Yes, there might be some out there. You can check fanfiction websites like Archive of Our Own (AO3). There are a large number of fan - created stories in the My Hero Academia fandom, and it's possible to find one with this particular pairing and plot. Just use the search function on the website and type in relevant keywords like 'Bakugou x Uraraka pregnant' to narrow down your search.