Deku breaks bones because, of course!

                                    

                                          
After that, Katsuki went to Takoba beach every day with Izuku to train, although Katsuki was doing more watching than anything else. At around the five month mark of Izuku's training, he used his quirk for the first time in his new form. 
The two boys were standing in front of a large metal filing cabinet. Izuku has his arm positioned so that his hand was at eye level and his middle finger poised to flick.
"What are you doing? You look like an idiot" Katsuki said helpfully.
"I've determined that this is the best way to avoid serious injuries. By focusing my power into my finger if worst comes to worst, I lose a didgett. No big deal." Izuku said, obviously oblivious to the fact that he had just been insulted. A bead of sweat ran down his temple as he clenched his jaw in anticipation. A tense silence fell over the beach.
"Nervous nerd?" Katsuki asked into the silence.
"Yeah" Izuku said with a breathy laugh.
"I'm not taking you to the hospital if things go wrong." Katsuki said, just as tense as the older boy.
"Well obviously, I'm still older than you, Kacchan" Deku said, rolling his eyes.
The nickname was one Izuku had started using for Katsuki when he was six and had since abandoned, except when he wanted to make the temperamental blonde tick.
As expected, Katsuki rose to the occasion, taking the bate.
"Don't call me that, you stupid deku!!! I'm not the one about to voluntarily dismember myself!!"
"Gee, thanks for the vote of confidence Kat. Now shut up so I can concentrate."
And so, they fell into tense silence again. 
After what felt like an eternity, but was only actually a few seconds, Katsuki couldn't take it anymore.
"OH MY GOD JUST DO IT ALREADY!!"
And so Izuku did.
.     .     .
Izuku fell his knees in the sand as the filing cabinet fell to the sand with a loud 'whoump' ten feet from where is started.
"Holy shit it worked!!!" Katsuki yelled, grinning and jumping up and down in excitement. Then, as an afterthought,he ran over the the green haired boy, who was still kneeling and clutching his hand.
"Hey Izu are you okay?! Did it come off?!"
In response Izuku turned around with a huge grin on his face and said triumphantly
"It's broken!"
"oH..." Katsuki responded, worrying for Izuku's mental stability.
Katsuki didn't get a chance to voice his concerns because before he knew it, Izuku was standing and wrapping his arms around Katsuki. It took Katsuki second to process what was happening and another to realize that Izuku, who at this point Katsuki had admitted to himself he had a crush on, was very close and very shirtless. 
"oH..." Katsuki said again, his whole head going so red it was practically glowing.
"Wait." Katsuki said, suddenly realizing yet another thing (good job Katsuki, we are all proud of you). "Izu, are you crying ?"
"Yeah, a little." Izuku said with a laugh, pulling away from the embrace and wiping at his face.
"Man, you would think being totally ripped would make you less of a crybaby." Katsuki mutterd, his face still tinged pink.
"Come on, I've got some bandages in my bag, and you didn't say that you wouldn't help me wrap up my injuries, only that you wouldn't take me to the hospital so, hurry up, this really hurts." Izuku said, still smiling 
"Whatever Deku. You still have a long way to go" Katsuki huffed, crossing his arms as Izuku walked towards their stuff 
"Ah Katsuki,  the ever supportive." Izuku called back, rolling his eyes, the smile never leaving his face.