Several centuries ago in the kingdom of Orabelle, a monster was created by a curse, and thirteen heroes gathered to slay it.
Each hero faced a different deadly trial, and lost were twelve heroes.
The thirteenth sought out help, fearing for his life. Seeking the counsel of the king and queen, he was only given the help of the princess.
They were only able to conquer the first trial, leaving twelve.
Once every century, the two of them - as well as the princess' loyal steed - would be reincarnated to conquer the next trial.
After eleven more reincarnations, twelve trials were completed, one left.
What if rimuru was instead reborn as a primordial demon the strongest in combat and intelligence.
He reincarnated just before Star king dragon Veldanava created the omniverse; it was nothing but a void, his soul being exposed just a little to turn null made his soul undergo a change. Making him an individual with a high evolutionary potential