"High School DxD Hero" is the fourth season of the "High School DxD" anime series, adapting the ninth and tenth volumes of the light novel series by Ichiei Ishibumi. The story continues the adventures of Issei Hyoudou, a high school student and member of the Occult Research Club at Kuoh Academy, who is also a reincarnated devil serving under Rias Gremory, the heir to the Gremory clan. The narrative delves deeper into the political and supernatural conflicts within the devil world, focusing on the escalating tensions between factions and the looming threat of powerful adversaries.

The season begins with the Gremory peerage preparing for the Azazel Cup, a prestigious tournament for devil teams to compete for ranking and prestige. Issei, now more confident in his abilities as a devil and the wielder of the Boosted Gear, trains rigorously alongside his comrades to strengthen their team. The tournament serves as a backdrop for exploring the dynamics between characters, their growth, and the alliances they forge. Key figures such as Rias, Akeno, Koneko, and Kiba play significant roles in the team's strategy and battles, showcasing their unique abilities and personal struggles.

A central plotline involves the introduction of new antagonists, including the malevolent Qlippoth organization, which seeks to disrupt the balance of power in the underworld. The group's leader, Rizevim Livan Lucifer, a descendant of the original Lucifer, emerges as a formidable foe, orchestrating schemes to destabilize the devil hierarchy. His actions lead to confrontations that test the resolve and strength of Issei and his allies. The season also explores the relationship between Issei and Rias, as well as his growing harem of female characters, including Asia Argento, Xenovia, and Irina Shidou, who each contribute to the team's efforts in their own ways.

The narrative balances action-packed battles with moments of character development and humor, maintaining the series' signature blend of supernatural intrigue and comedic elements. Themes of loyalty, ambition, and the pursuit of power are interwoven with the personal journeys of the characters, particularly Issei's evolution from a perverted yet determined teenager to a more mature and capable leader. The season concludes with significant developments in the overarching plot, setting the stage for future conflicts and challenges in the "High School DxD" universe.