After saving his master, Rias Gremory, from the Dimensional Gap, Issei Hyoudou, known as the Red Dragon Emperor and future Harem King, rejoins his high school routine with his Occult Research Club comrades: Yuuto Kiba, Asia Argento, Xenovia Quarta, and Irina Shidou. Their peaceful school trip to Kyoto takes a turbulent turn when local youkai attack, leading to the revelation of a kidnapped mystical fox and a framed accusation against the club. Now, Issei and his friends must defend the city, ensuring their trip's safety from imminent chaos. Meanwhile, back in Tokyo, Rias, accompanied by Akeno Himejima and Koneko Toujou, wrestles with unease at leaving Issei, pondering the true depth of her emotions that have troubled her for months.