Sometimes It’s a Good Hurt (смешанная)

“Kacchan’s so brave,” Izuku held the hand on Katsuki’s chin firmly and used his other hand to wipe the snot and tears away. “You’re so, so, so, brave for coming to look for help even if you know you could be in trouble. I promise that your sister is going to be just fine because you came to help her.”
Or
As the youngest of two omega children, Katsuki knows that he can't get married until after his older sister Ochaco does. That wouldn't bother him so much if she wasn't in love with an alpha who hasn’t so much as made a move and wouldn’t settle for anything less than the man she loves. So when the sole alpha child of the Midoriyas, Izuku, asks Mitsuki and Masaru for Katsuki's hand in marriage, he already knew they were going to tell him no; but why is Mitsuki offering them Ochaco's hand in marriage instead, and why is Izuku accepting?