Izuku blankly goes and opens it, then lights up when he sees the letter and katsuki cant help but smile. Izuku quickly opens it and reads with a smile. 

Dear Izuku, 

Seeing as you didnt leave it in your locker then im guessing its ok to write you more. Ive always thought that i wouldnt be able to talk to you like this, but im glad i have this. So how are you doing? I wish i could do something to help you, something that would keep him away from you so you wouldnt have to be in so much pain. I see that asshole Bakugou hitting and bullying you, who cares if you dont have a quirk, thats no reason to be such a dick, hes so pitiful. How can you handle being around someone like that? Stay strong. Write to you tomorrow. 

- Your secret admirer 

Izukus eyebrows furrow halfway through reading the letter and he puts it in his bag. He pulls out his own paper and pen. Katsuki can't see what he writes and Izuku shuts his locker, walking away. Katsuki waits for a moment, then rushes over to the locker, taking it out and reading. 

Kacchan isn't an asshole or a dick, and he is definitely not pitiful. Don't talk bad about him ever or I don't want to get your letters anymore. 

- Izuku Midoriya 

the writing is quick and messy, but the point is sent and received. Katsuki's heart skips a beat, and he puts the letter in his pocket, getting his stuff and walking home. After everything he has done to Izuku, how could he still say all that stuff? He feels giddy and like he's on cloud nine. The dream he has that night is... something. Izuku is caged below him in his arms, face red and his head turned away in embarrassment. 

"K-Kacchan.. You aren't the person you think you are so dont talk bad about yourself ever again or I'm not gonna be your boyfriend anymore, ok?" 

Katsuki leans down and kisses his lips softly. 

"Anything for you zuku." 

Izuku grins. 

"Thank you kacchan. I love you." 

Katsuki is in a bad mood after waking up from such an amazing dream, but all of that disappears when he sees izuku on his way into the school. The pink hair clips that he mentioned in his letter are in izukus hair. In. His. Hair. Katsuki nearly has a heart attack from the brain overload. He rushes to the lockers and puts the letter into izukus locker, hiding away again to watch him.