As summer break arrives at Kuoh Academy, Issei Hyoudou, the Red Dragon Emperor, reunites with the Occult Research Club for another round of adventures. Recognizing their lack of experience after a fierce battle against Vali and the Chaos Brigade, Rias Gremory and Azazel lead the club through rigorous training in the Underworld to enhance their skills. Amidst growing camaraderie within the team, Issei navigates new romantic entanglements with the club's female members. Meanwhile, their foes amass strength and numbers, culminating in a formidable threat with the arrival of Loki, the sinister God of Norse Mythology. Brace yourself for thrilling battles and the emergence of formidable devils in the captivating narrative of High School DxD BorN!