Well, Iida would probably have a very proper reaction. He might give Bakugou a stern talk about treating Deku right and being respectful on the date. Mina would be super excited and would start gossiping about it right away. She'd be all over Deku, asking him what he was going to wear and things like that. And Kaminari would probably make some silly jokes about it, like saying Bakugou was finally 'going soft' for Deku.
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.
One possible scenario is that Bakugou finally realizes his true feelings for Deku after a long time of denying them. He might plan a really elaborate date, like taking Deku to a special place that has significance for both of them, perhaps a place where they trained together when they were younger. It could be a really emotional moment when he asks Deku out, with Bakugou being uncharacteristically nervous.
Some characters might try to understand Deku's motives. Kirishima, who was close to Bakugou, would be angry at first but might also try to find out if there were any extenuating circumstances. However, many would be afraid of Deku, seeing him as a threat now that he has killed one of their own.
One key element is the resolution of their past conflicts. Since they had a lot of rivalry in the original story, in a friends - based fanfic, they need to address those issues. For example, Bakugou realizing his wrong attitude towards Deku.
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.
One great fanfic is 'The Road to Friendship'. It shows Bakugou slowly realizing Deku's worth and them building a bond through various challenges at UA. It has some really heartwarming moments like when they team up in a training exercise and start to understand each other better.
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.
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.
Their friends' reactions could be quite mixed. Ron might be a bit jealous, especially since he has his own complicated feelings towards Hermione. He might not show it directly, but there could be some underlying tension. Harry, on the other hand, would probably be supportive. He's always been more open - minded and would see it as a chance for his two friends to have a good time. Ginny might be a bit surprised at first, but then she'd probably be excited for her brother and Hermione.
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.