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.
Well, in such a fanfiction, it often explores a different side of Deku being a villain and his relationship with Todoroki. It could be about how their dynamic changes from the original story. Maybe Deku as a villain has different motives and goals that somehow involve Todoroki, like trying to use Todoroki's power for his own evil plans or trying to turn Todoroki to his side.
Power imbalance is often a theme. Deku might gain new, more dangerous powers as a villain, and Todoroki has to figure out how to deal with that. There could also be a theme of trust. Since Deku is a villain, Todoroki has to decide whether to trust him or not. And if he does trust him, it could lead to all sorts of complications in the story.
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.
One possible plot is that Bakugou has been secretly in love with Deku for a long time. He observes Deku's kindness and growth, and it makes his heart flutter. He decides to propose when they are alone one day. He might start by reminiscing about their journey together, from being rivals to becoming something more, and then pop the question.
The main characters are Bakugou and Deku. Bakugou is often portrayed as a brash and confident character, while Deku is kind - hearted and determined. In this fanfic, their relationship takes a romantic turn with Bakugou being the one to propose.
I haven't come across one, but you could try looking on specialized comic websites or social media groups focused on comics. Maybe someone there knows if such a comic exists.