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.
In the fanfic, there might be a moment where Bakugou is seriously injured but still tries to encourage Deku to keep going and not worry about him. This selfless act of putting Deku's well - being and future above his own pain is a strong indication of his love. Also, when Bakugou starts to train with Deku privately to help him improve his skills, it shows that he wants to see Deku succeed and is willing to invest his own time in it.
Bakugou may prove his love by being protective. He might put himself in danger to save Deku. In many stories, this kind of self - sacrifice is a strong indication of love. Also, he could start to understand Deku's dreams and support him in achieving them, which is a deeper form of love than just friendship.
The relationship could start with hatred. Bakugou may initially be enraged that Deku has become a villain. But as time passes, he starts to see the reasons behind Deku's transformation, which could lead to a more complex relationship.
At first, it could be extremely strained. Deku might be terrified of Bakugou and avoid him at all costs. But as the story progresses, if Bakugou realizes his mistake, he could start trying to make it up to Deku. Deku, on the other hand, might be hesitant to accept Bakugou's apologies at first, but over time, they could start to rebuild a more positive relationship based on mutual respect.
Bakugou's character might develop by becoming more empathetic. At first, he may be his usual brash self, but as he sees Deku in distress, he starts to understand the importance of being kind. So he grows in his ability to show compassion.
Growth is also a prevalent theme. Both characters are on a journey of self - discovery and improvement, and fanfics usually show how they grow both as individuals and in relation to each other. For example, Bakugou learning to control his temper and Deku becoming more confident.
One common theme is rivalry. Their intense competition to be the best hero is often explored, like in many fanfics where they constantly try to outdo each other in training or in real battles. It shows their determination and drive.
Deku might be initially shocked. He's used to Bakugou's aggression, but an actual injury is different. He could be in pain and disbelief at first. Then, he might try to downplay it, especially if he doesn't want to cause trouble for Bakugou, because Deku is generally a very forgiving character.