Flashfreeze Heatwave (膨冷熱波 Bōrei Neppa?) is a Super Move performed by Shoto Todoroki using his Half-Cold Half-Hot Quirk.
This technique starts after Shoto uses his ice to thoroughly chill the air in the area around him. By switching to his fire, Shoto rapidly heats the air around him and expands it.
This environment allows Shoto to release a superheated blast that devastates anything on its path.
Shoto first used this move to defeat Izuku Midoriya in the U.A. Sports Festival. The technique gets its name when Shoto uses a smaller-scale version of the attack to subdue villains. 
My Hero Academia Manga and Anime: Chapter 40 and Episode 23.
My Hero Academia Manga: Chapter 219.