High School DxD BorN

After their clash with Vali and the Chaos Brigade, the members of the Occult Research Club realize how badly they need to grow stronger. Rias and Azazel use the summer break to take the group into the Underworld, where each member undergoes training aimed at personal weaknesses while Issei works to master the power of the Red Dragon Emperor.

They receive little time to enjoy the results. Their enemies continue gathering strength, and Loki, the evil god of Norse mythology, emerges with a threat capable of drawing multiple supernatural factions into another conflict. Issei's home life with Rias and the other girls remains as crowded as ever, but the danger ahead requires the entire group to mature into a genuinely dependable team.