A great Deku and Eri fanfiction could be set in a future where Eri has grown up a bit. She and Deku go on a mission together to rescue some hostages. Deku is proud of how far Eri has come and they work together as a great team.
The theme of family or a found family is also common. Deku and Eri can be seen as forming a sort of family unit. Deku takes on a big - brother or father - like role for Eri, and they develop a deep bond that is similar to what one would find in a family.
Some Tumblr blogs are dedicated to sharing and recommending fanfiction. You could search for My Hero Academia fanfic blogs and then look specifically for Deku and Eri stories. They might also have reviews or summaries to help you decide which ones to read.
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.
There's also 'Deku and Eri's Adventures'. In this fanfic, they go on various adventures together in the world of heroes. It's full of exciting action scenes and also some really sweet moments between the two characters.
He might cry a lot. Deku is very emotional, and being cheated on would be a very painful experience for him. He could also get angry, which is rare for him, but this situation would be so unjust that he might not be able to hold it in. He'd probably start to question his self - worth too, thinking that there was something wrong with him that made his partner cheat.
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.
Well, some might be really amazed. They could see a new side of Deku that they never knew before. His singing might show a different level of confidence or a hidden talent, so they would probably cheer him on.
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.