Horikoshi has a comment on "Midoriya Izuku and Bakugou Katsuki" at the exhibition with a lot of panels on display featuring key scenes they are in.
He says that writing their dynamic was challenging because one single wrong move could cause everything to fall apart, and this applies to not just them, but real life situations among people around the world in general.
Deku initially thought of him as a jerk but still admired his strength, and that was hard to convey as people don't usually look at someone they dislike from different perspectives. However, their shared admiration for All Might was what helped them move forward.
For Bakugou, at first Horikoshi thought his character end goal was to be able to apologize to Deku, but as he kept writing, he realized that wasn't really the goal after all. Bakugou is a type of character not ruled by logic, so it was very difficult to portray.