High School DxD EX

High School DxD EX (ハイスクールD×D EX Haisukūru D×D EX) is a six part special novel released with the Blu-Ray volumes of the third anime series, High School DxD BorN.

Summary
The Occult Research Club 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.

Main Characters

 * Ex Gremory (イクス・グレモリー Ikusu Guremori): The main character of the story and son of Issei Hyoudou and Rias Gremory. He wields an artificial version of the Boosted Gear and a crimson sword, Galatine III.
 * Kurenai Himejima (姫島 紅 Himejima Kurenai): The eldest of the siblings and son of Issei and Akeno Himejima. He inherited the abilities of the Himejima bloodline and his grandfather. He's also the person that created the Artificial Boosted Gear for his brother Ex.
 * Zen Quarta (漸・クァルタ Zen Kuaruta): Son of Issei and Xenovia Quarta, wielder of the Durandal IV.
 * Shirayuki : Daughter of Issei and Koneko Toujou. A Senjutsu user.
 * Kurobara : Daughter of Issei and Kuroka. A Senjutsu user.
 * Airi Hyoudou: The second eldest of the siblings, daughter of Issei and Asia Argento.
 * Shin Shidou: Son of Issei and Irina Shidou.
 * Robertina Hyoudou: Daughter of Issei and Ravel Phenex. She respects her father the most out of her siblings.
 * Helmwige: Daughter of Issei and Rossweisse.
 * Ernestine Galnstein: Daughter of Issei and Elmenhilde Galnstein, she travels to the past with her father.

Antagonist

 * Loki (ロキ): The Evil God of Norse who returns to the past after cursing Asia. He teams up with the beings from the other world UL to change the past.
 * UL: Mechanical beings from the other world.