High School DxD EX

High School DxD EX is the 4th season of the High School DxD anime series which is based off of the light novels by Ichiei Ishibumi. This season based off the six-part special novel series of the same name.

Plot
A few months after the events of the last season, the ORC faces off against invaders known as Underworld Lifeforms led by Loki that has travel from the future, however also from the future comes a surprise visit by Issei's children.