More than 100 years ago, in the city of Tokyo, a human boy named Nobi Nobita had been abducted by unknown forces, those same forces that took him to a destination called Illumia, on the Planet Bessekai.
Many years ago after that event, Bessekai was created as a personal project by Professors Ruyami and Ab, who created a world from scratch based on medieval mythology, fantasy and RPG with an energy source that allows any creature to use artificial magic, that energy was called "Mana", the project was called ISEKAI Project, they were from the 22nd century but they made their project in the past, which at first would serve to give humans on Earth a second chance at life through adventure and fantasy.
The project was going smoothly until one of the scientists, Professor Ab, decided to take over the project by transforming himself into a mutation like an arch-demon and proclaimed himself "Abaddon, the Demon King."
With this event, Professor Ruyami, who transformed into a kind of goddess of her own energy element and who became known as "Goddess Ruya", summoned the mind of a deceased person from Earth so that he could reincarnate into Bessekai to momentarily defeat the Demon King, who decided to rest for many years to once again want to conquer both Bessekai and the Earth.
One of the other projects called the Besse-Earth Temporal Bridge that connected Bessekai to Earth, was closed by Ruyami and the one known as the "Hero of Illumia" to prevent the Demon King from trying to infiltrate Earth, causing a temporal alteration between both destinations where in one of them the time was faster, keeping the key as a shine in two individuals so that one day after defeating the Demon King completely, the bridge could be reestablished for a new objective: The unification between both worlds in order for them to develop thanks to the elements of the other.
Ruyami also appointed the mana to choose someone to change the course of the last battle against the Demon King, being the balance between good and evil. Exactly that was the abducted boy mentioned at the beginning, this could take the course of helping the new hero of Illumia or helping the Demon King, described in the professor's "prophecies".
The 11-year-old boy, despite being afraid and not understanding the environment of that world, decided to go to the side of the Hero of Illumia, and thanks to his friends and one of the nanny robot cats, they were able to replace a legendary weapon that helped the first hero. The boy created his own legend in Illumia, helping whoever needed it. Being a swordsman of the lightning element, the people of Illumia decided to nickname him the "Lightning Swordsman" and then be recognized as the "Summoned One", winning along with the Hero Dekisugi's team to the Demon King forever and his 7 elemental generals who weren't only able to reactivate the bridge resetting the time space, but also tried to invade the world. But thanks to the Summoned One and the Hero of Illumia, Professor Ab was banished from a world that he wanted to dominate.
After reestablishing Bessekai, the Summoned One decided to stay in Illumia to help with the project of turning Illumia into a good place for unification, it took him years but he had achieved it by trapping the rest of the generals who were scattered across the continent. The Besse-Earth bridge that had been frozen to prevent monsters from entering Earth, was reopened when the Bessekai-Earth Treaties were official, thus beginning the unification, some time later, the "power of mana" was adapting to Earth, allowing the Terrans to use the 7 elemental powers of Illumia, while Illumia gradually became a modernized Empire without leaving aside fantasy adventures.
The Summoned One Nobita not only changed the future of the Earth, but also saved a project which improved the quality of both worlds, the Summoned One became the Guardian of Illumia to protect and improve that planet. Later when he became an adult, he married the Princess of Humans, later becoming the King of Inuma in Bessekai, one of the 4 kings of Illumia. His descendants gradually settled into those living in Illumia and those living in Tokyo until reaching the current 22nd century.
Without a doubt it can be said that thanks to Nobi Nobita, the future of both planets ended up developing more, thus becoming one of the most important figures in the history of both Earth and Bessekai.