Denki Kaminari charges his body with over a million volts of electricity before releasing it indiscriminately around him. The attack has enough power to take down various opponents at once, but can be blocked by halting the electric current.
Denki usually suffers from short circuiting his brain after using this attack. However during the Cavalry Battle, Denki was able to use the move more than a few times before jamming himself. 
Ibara Shiozaki was able to block this attack using her hair, and Momo Yaoyorozu has used a thick sheet of insolation to protect herself. 
This move is named Indiscriminate Shock 1,300,000 volts in the Funimation English Dub.