Issei Hyodo and the Occult Research Club face a new crisis when the ancient peace treaty among Devils, Angels, and Fallen Angels fractures. A rogue faction known as The Eclipse Vanguard begins hunting down Sacred Gear users globally to harvest their power and build an artificial deity.
To protect Kuoh Academy and the Underworld, Rias Gremory expands her peerage, forcing Issei to mentor a new generation of reincarnated low-class Devils. This changes Issei’s dynamic from a reckless fighter into a chaotic but dedicated mentor. As the Vanguard attacks, Issei discovers a hidden evolution within his Boosted Gear—the Overdrive Break—which allows him to temporarily manifest the true, unrestricted power of the Welsh Dragon, though at the cost of intense physical strain.
The narrative balances high-stakes supernatural warfare with the series' signature ecchi comedy, harem shenanigans, and mythological world-building. Issei must juggle his dream of becoming a Harem King with his new responsibilities, while working alongside Vali Lucifer to stop a cosmic threat capable of destroying all three factions.
