After the Kitauji High School concert band's auditions for club member participation in the Kyoto Prefectural Concert Band competition, 10 members fail to pass the strict evaluation. Despite being unable to play with the rest of the wind ensemble, the group—who decide to name themselves Team Monaka—is determined to support their peers in any way possible until the day of the competition. From carrying supplies to creating monaka-shaped good-luck charms, Team Monaka's efforts prove to be pivotal for the unforgettable, bittersweet summer in the concert band's journey toward nationals.

Yuuta Hoshitani enrolls in the prestigious Ayanagi Academy in hopes of finding the high school student who inspired him. The academy is well-known for producing exceptional musical talent, but students must first compete for acceptance into the Musical Department. At the top of the department is the Kao Council—a group of third-year students who possess a great deal of influence over the school and admission into the department. The fastest route to entering the department for Hoshitani is to find a way into a Star Team, which would allow him to be taught by a member of the Kao Council. After catching the eyes of Itsuki Ootori, Hoshitani finds himself under the tutelage of the Kao Council's most eccentric member. Alongside him on Team Ootori is his roommate, Tooru Nayuki, fledgling Kabuki actor Kakeru Tengenji, the quiet Shuu Kuga, and Kaito Tsukigami, the younger brother of famous Ayanagi alumni Haruto. As Hoshitani struggles with his lack of talent, his teammates must also overcome their shortcomings. Facing opposition from other talented Star Teams, including the other four members of the Kao Council, Team Ootori must carve their own path as they aim to perform in the Ayanagi Festival.

The Red Dragon Emperor, Issei Hyoudou, and the Occult Research Club are back in action as summer break comes for the students of Kuoh Academy. After their fight with Issei’s sworn enemy, Vali and the Chaos Brigade, it is clear just how inexperienced Rias Gremory's team is. As a result, she and Azazel lead the club on an intense training regime in the Underworld to prepare them for the challenges that lie ahead. While they slowly mature as a team, Issei will once again find himself in intimate situations with the girls of the Occult Research Club. Meanwhile, their adversaries grow stronger and more numerous as they rally their forces. And with the sudden appearance of Loki, the Evil God of Norse Mythology, the stage is set for epic fights and wickedly powerful devils in High School DxD BorN!

Unaired anime episode bundled with the limited edition of High School DxD DX.2.