Volume 1 of the Demons of Onigashima side story. "A dance of a thousand cherry blossoms. The Ronin of a Hundred Demons dances as a god of flame as a thousand cherry blossoms burn around him. He who commands many demons shall also command the fate of Japan." The heat of summer.. a time for vacations. And even heroes need vacations.. even if an organization called GREMLIN is currently the world, they work slow.. and Ben and Mikoto need down time. Grandpa Max decides it's high time for another traditional Tennyson Family Summer Vacation, in other words, running on a country tour in an old junky RV called the Rust Bucket. However, this time it's not an exploration of the States, but of Japan. Little do Ben, Kuroko, Mikoto and Max know however.. that they're about to get more of Japan than they bargained for.. The gods of Japan are fickle, and the monsters and demons of Onigashima are hungry. Demons and Aliens clash. Toaru Kagaku no Omnituriksu the Demons of Onigashima, is about to begin.

After the defeats of Terra of the Left and Vento of The Front by Ben Tennyson, Acqua of the Back sends out a warning that he intends to destroy the Omnitrix and the one wielding it. In response, The Church of England sends the Amakusa Church to provide protection while the Plumbers send in forces of their own. But can anyone protect Ben from a Saint Class magician powerful enough to even defeat the Ultimate Aliens with ease?

(Chronology: Daihaseisai Arc of A Certain Magical Index.) The Daihaseisai is here! A festival event where all the schools in Academy City compete with each other in sporting events.. a festival even more popular then the World Cup. Espers from all over are encouraged to use their abilities. Meanwhile, the Board of Directors have taken an interest in Ben Tennyson after his success in defeating the Eigth Level 5 Impulser.. the Level 5 whose power was impossible to categorize.. and Aleister Crowley, the City administrator has taken up a rather sinister plan to find out how to test this new weapon in his arsenal... attract the most powerful conquerer in the Galaxy to do battle with that boy. Meanwhile, Ben is starting to realize the possibility that he might have feelings for Mikoto, but is scared of what it might mean... And while Mikoto feels the same way, she doesn't know what to do with those feelings.. But of course.. all things must eventually converge and resolve, for better or for worse.

Academy City. A large city in Japan that is comprised completely of research centers, colleges, high schools, middle schools, and elementary schools. 81 percent of it's population is comprised of students while 60 percent of students are super powered psychics created through Academy City's power development program called Espers. Mikoto Misaka is the third strongest Esper out of that 2.1 billion that dwell in Academy City, being also a prestigious student at the most high class all girl's school in the entire world. Naturally, having such high powers, she has faced many weird phenomenon within the city known for the weird and scientifically advanced. However.. her knowledge about the universe is challenged when she meets a particularly weak esper named Ben Tennyson, whose been living on the streets because he couldn't afford the dorm. And as Mikoto will soon discover.. Ben's true powers.. completely unrelated to his esper ones... are quite out of this world...literally.. ( Also known as とある科学のオムニトリックス Toaru Kagaku no Omunitorikkusu.)