Now there's a mysterious Mask before James Blood, and the man behind it is one that shouldn't exist. What is the mystery surrounding this mask...? So begins an action-packed crime story set in a beautiful city!

After rescuing his master, Rias Gremory, from the Dimensional Gap, Red Dragon Emperor and aspiring Harem King Issei Hyoudou can finally return to his high school activities alongside fellow members of the Occult Research Club: Yuuto Kiba, Asia Argento, Xenovia Quarta, and Irina Shidou. The group soon embarks on a school trip to Kyoto. While peacefully visiting a temple thanks to Rias' spell, an attacking group of local youkai breaks the calm atmosphere. Once the altercation ends, the club learns that the mythical nine-tailed fox that protected the city was abducted and that someone has framed them for the act. Issei and his friends will now have to fight to protect the city and save their school trip from a planned disaster! In the meantime, Rias, who had to stay in Tokyo with Akeno Himejima and Koneko Toujou, grows increasingly restless to have left the perverted Issei alone with the other girls of the Occult Research Club. Beyond this vague anxiety, what is the exact nature of the feelings Rias has been struggling with for the past few months?

The year is 1991, and arcade video games are the latest craze. Becoming a professional gamer is a far-fetched dream in an industry that has yet to spread its influence. Yet, that is the path sixth-grader Haruo Yaguchi wants to pursue. His aptitude for video games has earned him respect in local arcades and bestowed him with confidence and pride, both of which are shattered when fellow classmate Akira Oono easily defeats him in Street Fighter 2. Akira is rich, pretty, and smart—as close as can be to a perfect girl. But Haruo had never cared about these things as, despite his multiple shortcomings as a person, his supremacy in video games was, in his mind, undisputed. So, now that someone has appeared who can rival him, part of Haruo cannot help but loathe her. Another part, however, itches for somebody who can compete with him on equal terms, and Akira is more than capable.

In professional sumo, there are no weight classes. It's a savage sport where the strongest survive, and anyone willing to test their mettle can step into the ring. There is, however, a minimum size requirement to be a pro sumo wrestler, and young Hinomaru Ushio, incredibly talented and hardworking though he may be, does not meet that requirement. This small boy has big dreams of reaching the highest class of sumo, Hinoshita Kaisan. The only way he could possibly go pro is if he becomes the High School Yokozuna, a title given to the strongest wrestler in high school tournaments. Ushio is under a lot of pressure, as well as a time limit. If he can't show off his skills in the high school tournaments, he may lose his chance to go pro permanently, and the odds are stacked against him. Instead of enrolling in Ishigami High, the best school for sumo in Japan, he enrolls in Odachi High and must build a sumo club from the ground up with the one devout member Shinya Ozeki. Odachi High is the true underdog of the sumo world, but Ushio has to push forward with all his strength if he is going to make it professionally.