Izuku Was Bullied By His Friends And His Sister (Class 1-A are All Childhood Friends). One Day they Went too far and Raiga Was Killed as His Soul Passes On to the Cardinal World He was Reincarnated into a Kijin he Along With Mika Satomi Who was Reincarnated into a Slime woke up in the Cave Where the Otaku Storm Dragon Veldora was Sealed watch as two Reincarnators Changed the Whole Cardinal World. (Izuku Was Renamed as Raiga Tempest and Mika was Renamed as Rimuru Tempest)
Rimuru Has All the Same Skills In Canon
While Raiga Was Reincarnated with the Unique Skills
Unique Skill Tyranny
Unique Skill Bravery
Unique Skill Super Sage
Unique Skill Boost
Unique Skill Divide
Central/Cardinal World
The Central World (基軸世界 kijiku sekai, lit. "Central Axis World"?) is the Multiverse in which the That Time I Got Reincarnated as a Slime series primarily takes place.
Background
The original universe out of the many universes created by Star-King Dragon Veldanava. It's a world of "chaos" that has the mixed properties of both a spiritual world and a physical world. Many different objects and beings from other universes often find themselves winding up in the central world by chance, but getting out is a substantially more difficult task with the notable exception of the spirit realm and demon realm, which have "gates" going to and from.
Main Planet
Continents
Magic Continent
The Magic Continent (魔大陸 Ma tairiku?) is the central continent where most of the series events take place. On the far west, there are the "Barren Lands", a great expanse of inhospitable sandy desert contaminated with magicule radiations where the ancient ruin of 'Soma' is located and the territory of Demon Lord Dagruel, on its border lies the Holy Empire Ruberios, a rich land and the territory of Demon Lord Luminous Valentine as well as the home of the Western Holy Church.
In the center of the continent lies a great collection of countries collectively referred to as the 'Western Nations', as well as the Jura Forest which contains the Jura Tempest Federation and is the abode of Storm Dragon Veldora. Both are considered the territory of Demon Lord Rimuru, although he's only publicly the ruler of the Tempest Federation. There's also the 'Canaat Mountain Range' to the north, a great expanse of mountains ruled on the surface by the Dragon Lords who reside in the 'Dragon Roost' at the peak of the tallest mountain, and ruled underground by the Armed Nation of Dwargon. And at the southern border of Jura Forest is the Sorcerer's Dynasty Sarion, a collection of 13 elven states that swear allegiance to their divine emperor Elmesia El Ru Sarion, but otherwise act independently to each other. Its "capital" is the state of El-Ru where the emperor and his family reside.
In the eastern border of the Jura Forest lies a collection of demi-human and majin populated states collectively the territory of Demon Lord Milim Nava. Its 'Capital' is the unnamed city currently under construction at the site of the former capital of the Beast Kingdom Eurazania. And finally to the far east lies the Nasca Namrium Ulmeria United Eastern Empire or more simply 'Eastern Empire', an expansionist empire made up of over 100 cities with a population of over eight-hundred million people. In the empire, people of all races are accepted without prejudice as long as they submit themselves to the emperor and anybody can obtain political power by joining the military. It is a land of "might makes right", ruled by its eternal emperor Rudra Nam Ul Nasca. Its capital is called 'Nasca' and is located next to a great holy mountain said to house the empire's guardian deity, Scorch Dragon Velgrynd.
