For those not getting it, it's a reference to one of the best voice acting performances. An over two minute long single (!) take in an episode of When Supernatural Battles Became Commonplace - Inou-Battle wa Nichijou-kei no Naka de.
If you enjoy listening to great seyus, and you don't mind a silly fantasy anime about superpowered highschoolers, then it's worth watching the season of this anime just for that scene. It really is great.